U.S. patent number 6,337,957 [Application Number 09/597,405] was granted by the patent office on 2002-01-08 for image forming apparatus and developing device with improved self toner density control.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Tsuyoshi Imamura, Mikio Ishibashi, Shunji Katoh, Shinichi Kawahara, Tokuya Ohjimi, Kazuhisa Sudo, Shinji Tamaki, Junichi Terai, Kiyonori Tsuda, Masayuki Yamane, Hideo Yoshizawa.
United States Patent |
6,337,957 |
Tamaki , et al. |
January 8, 2002 |
Image forming apparatus and developing device with improved self
toner density control
Abstract
A developing device includes a developer bearing member
including an internal magnetic field generating device and
configured such that a surface thereof moves to carry and convey a
developer including toner and carrier. A developer regulating
member regulates a quantity of the developer carried and conveyed
by the developer bearing member toward a developing area, and a
developer accommodating unit accommodates the developer regulated
to be conveyed toward the developing area by the developer
regulating member. A toner accommodating unit includes a toner
supplying opening opposing a surface of the developer bearing
surface of the developer bearing member at a position adjacent to
and upstream of the developer accommodating unit in a developer
conveying direction. The toner in the toner accommodating unit is
taken into the developer on the developer bearing member based on a
toner density of the developer on the developer bearing member by a
movement of the developer with a conveyance of the developer on the
developer bearing member. The developing device further includes a
peeling off member that opposes, without contacting, a surface of
the developer bearing member in the developer accommodating unit so
as to peel off an upper layer part of the developer carried and
conveyed by the developer bearing member.
Inventors: |
Tamaki; Shinji (Tokyo,
JP), Imamura; Tsuyoshi (Sagamihara, JP),
Yoshizawa; Hideo (Urawa, JP), Terai; Junichi
(Yokohama, JP), Yamane; Masayuki (Yokohama,
JP), Tsuda; Kiyonori (Yokohama, JP), Sudo;
Kazuhisa (Kawasaki, JP), Kawahara; Shinichi
(Tokyo, JP), Katoh; Shunji (Sagamihara,
JP), Ishibashi; Mikio (Yokohama, JP),
Ohjimi; Tokuya (Kawasaki, JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
|
Family
ID: |
27553419 |
Appl.
No.: |
09/597,405 |
Filed: |
June 21, 2000 |
Foreign Application Priority Data
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Jun 21, 1999 [JP] |
|
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11-174693 |
Jul 1, 1999 [JP] |
|
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11-187727 |
Jul 1, 1999 [JP] |
|
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11-188219 |
Sep 22, 1999 [JP] |
|
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11-269348 |
Sep 27, 1999 [JP] |
|
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11-272551 |
May 1, 2000 [JP] |
|
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12-133005 |
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Current U.S.
Class: |
399/29;
399/258 |
Current CPC
Class: |
G03G
15/09 (20130101); G03G 15/081 (20130101); G03G
2215/0634 (20130101) |
Current International
Class: |
G03G
15/09 (20060101); G03G 15/08 (20060101); G03G
015/08 () |
Field of
Search: |
;399/258,260,29,27
;222/DIG.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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8-185052 |
|
Jul 1996 |
|
JP |
|
8-278695 |
|
Oct 1996 |
|
JP |
|
10-198171 |
|
Jul 1998 |
|
JP |
|
10-232540 |
|
Sep 1998 |
|
JP |
|
11-044996 |
|
Feb 1999 |
|
JP |
|
Primary Examiner: Grainger; Quana M.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed as new and is desired to be secured by Letter
Patent of the United State is:
1. A developing device, comprising:
a developer bearing member including an internal magnetic field
generating device and configured to carry and convey a developer,
including toner and carrier, on its surface;
a developer regulating member configured to regulate a quantity of
the developer carried and conveyed by the developer bearing member
toward a developing area;
a developer accommodating unit configured to accommodate the
developer regulated to be conveyed toward the developing area by
the developer regulating member; and
a toner accommodating unit including a toner supplying opening
opposing a surface of the developer bearing member at a position
adjacent to and upstream of the developer accommodating unit in a
developer conveying direction, wherein the toner in the toner
accommodating unit is taken into the developer on the developer
bearing member based on a toner density of the developer on the
developer bearing member by a movement of the developer with a
conveyance of the developer on the developer bearing member;
and
a peeling off member opposing, without contacting, a surface of the
developer bearing member in the developer accommodating unit and
configured to peel off an upper layer part of the developer carried
and conveyed by the developer bearing member.
2. A developing device according to claim 1, further
comprising:
a second developer regulating member located between the toner
supplying opening of the toner accommodating unit and the developer
accommodating unit and configured to regulate a quantity of the
developer carried and conveyed by the developer bearing member
toward the developer accommodating unit from the toner supplying
opening of the toner accommodating unit, and
wherein a gap between the second regulating member and a surface of
the developer nearing member is set such that an amount of the
developer regulated by the second developer regulating member
increases as the toner density of the developer on the developer
bearing member increases.
3. A developing device according to claim 2, wherein a relation
0<Gh<Gd2 is satisfied, wherein Gh is a gap between the
peeling off member and the surface of the developer bearing member
and Gd2 is the gap between the second developer regulating member
and the surface of the developer member.
4. A developing device according to claim 2, wherein the magnetic
force generating device is configured so as not to have a magnetic
pole between a position opposing the peeling off member and a
position opposing the second developer regulating member.
5. A developing device according to claim 4, wherein a magnetic
flux density on a surface of the developer bearing member from the
position opposing the second developer regulating member and the
position opposing the peeling off member is such that the developer
is carried on the surface of the developer bearing member by a
magnetic force.
6. A developing device according to claim 1, wherein:
the peeling off member comprises a roller-like shaped rotating
member; and
the developing device further comprises a rotation driving device
configured to drive the peeling off member to rotate such that a
surface of the peeling off member moves, at a position opposing the
developer bearing member, in a direction opposite a direction in
which the surface of the developer bearing member moves.
7. A developing device according to claim 6, wherein the peeling
off member includes a magnetic member.
8. A developing device according to claim 7, wherein:
the peeling off member is supported at its both ends in a direction
perpendicular to a direction of conveying the developer on the
developer bearing member; and
a diameter of the peeling off member at its center in the direction
perpendicular to the developer conveying direction is smaller than
diameters at both ends of the peeling off member.
9. A developing device according to claim 1, wherein:
the peeling off member extends in a direction perpendicular to a
direction of conveying the developer on the developer bearing
member and includes a magnetic member; and
the developing device further comprises a rotation driving device
configured to drive the peeling off member to rotate such that a
surface of the peeling off member moves, at a position opposing the
developer bearing member, in a direction opposite a direction in
which the surface of the developer bearing member moves.
10. A developing device according to claim 1, wherein:
the peeling off member extends in a direction perpendicular to a
direction of conveying the developer on the developer bearing
member and a magnetic pole is magnetized at a surface thereof;
and
the developing device further comprises a rotation driving device
configured to drive the peeling off member to rotate such that a
surface of the peeling off member moves, at a position opposing the
developer bearing member, in a direction opposite a direction in
which the surface of the developer bearing member moves.
11. A developing device according to claim 10, wherein:
the peeling off member comprises a roller-like shaped rotating
member; and
a plurality of magnetic poles are magnetized at a surface of the
peeling off member.
12. A developing device according to claim 11, wherein the
plurality of magnetic poles are magnetized such that S and N poles
are alternately arranged.
13. A developing device according to claim 12, wherein each of the
plurality of magnetic poles is magnetized liearly in an extending
direction of a rotation axis of the peeling off member.
14. A developing device according to claim 11, wherein the
plurality of magnetic poles are magnetized such that a plurality of
N and S poles alternately arranged in the extending direction of
the peeling off member are arranged in a circumferential direction
of the peeling off roller.
15. A developing device according to claim 6, wherein the rotation
driving device drives the peeling off member to rotate at varied
speeds.
16. A developing device according to claim 15, further
comprising:
a control device configured to control the rotation driving device
according to an image portion ratio of an image for printing.
17. A developing device according to claim 15, further
comprising:
a temperature measuring device configured to measure a temperature
inside of the developing device; and
a control device configured to control the rotation driving device
according to a result of measuring the temperature with the
temperature measuring device.
18. A developing device according to claim 15, further
comprising:
a humidity measuring device configured to measure a humidity inside
of the developing device; and
a control device configured to control the rotation driving device
according to a result of measuring the humidity with the humidity
measuring device.
19. A developing device according to claim 15, wherein the rotation
driving device is controlled such that a relation 0.5<T/S<1.5
is satisfied, wherein S(mm/s) is a linear speed of the developer
bearing member and T(mm/s) is a linear speed of the peeling off
member.
20. A developing device according to claim 6, wherein a surface of
the peeling off member is coarse.
21. A developing device according to claim 7, wherein:
the peeling off member comprises a magnetic member; and
the peeling off member opposes a peak position of a magnetic flux
density distribution in a direction of a normal line on a surface
of the developer bearing member.
22. A developing device according to claim 21, wherein
a magnetic flux density distribution in a direction of a normal
line at a circumferential surface of the peeling off roller
opposite a side thereof opposing the developer bearing member is
greater than 5 mT.
23. A developing device according to claim 21, further
comprising:
a second developer regulating member located between the toner
supplying opening of the toner accommodating unit and the developer
accommodating unit to regulate a quantity of the developer carried
and conveyed by the developer bearing member toward the developer
accommodating unit from the toner supplying opening of the toner
accommodating unit; and
wherein a relation MF2<(2/3)MF1 is satisfied, wherein MF1 is a
magnetic force received by the developer on the developing bearing
member at a position opposing the peeling off roller and MF2 is a
magnetic force received by the developer on the developing bearing
member at a position opposing the second developer regulating
member.
24. A developing device according to claim 1, wherein:
the peeling off member includes a scooping surface extending in a
direction perpendicular to a direction of conveying the developer
on the developer bearing member configured to scoop an upper layer
of the developer on the developer bearing member to be peeled off
the developer bearing member; and
a scooping angle of the scooping surface of the peeling off member
relative to a tangent line in a direction of conveying the
developer at a surface of the developer bearing member is greater
than 90 degrees.
25. A developing device according to claim 1, wherein the peeling
off member is a grid-like flat plate.
26. A developing device, comprising:
a developer bearing member including an internal magnetic field
generating device configured to carry and convey a developer,
including toner and carrier, on its surface;
a developer regulating member configured to regulate a quantity of
the developer carried and conveyed by the developer bearing member
toward a developing area;
a developer accommodating unit configured to accommodate the
developer regulated to be conveyed toward the developing area by
the developer regulating member; and
a toner accommodating unit including a toner supplying opening
opposing a surface of the developer bearing member at a position
adjacent to and upstream of the developer accommodating unit in a
developer conveying direction, wherein the toner in the toner
accommodating unit is taken into the developer on the developer
bearing member based on a toner density of the developer on the
developer bearing member by a movement of the developer with a
conveyance of the developer on the developer bearing member;
and
a developer stirring member opposing, without contacting, a surface
of the developer bearing member in the developer accommodating unit
at a position adjacent to the toner accommodating unit so as to
stir a part of the developer carried and conveyed by the developer
bearing member, where the toner is taken into the developer from
the toner accommodating unit,
wherein the developer stirring member comprises a comb-like member
having comb teeth at one end thereof.
27. A developing device according to claim 26, further comprising a
second developer regulating member located between the toner
supplying opening of the toner accommodating unit and the developer
accommodating unit and configured to regulate a quantity of the
developer carried and conveyed by the developer bearing member
toward the developer accommodating unit from the toner supplying
opening of the toner accommodating unit.
28. A developing device according to claim 26, wherein
a relation 0<Gk<Gd is satisfied, wherein Gd is a gap between
a surface of the developer bearing member and the second developer
regulating member and Gk is a gap between a surface of the
developer bearing member and a tip end of the comb teeth of the
comb-like member.
29. A developing device according to claim 26, wherein
an interval between tip ends of the comb teeth of the comb-like
member is less than 5 mm.
30. A developing device, comprising:
a developer bearing member including an internal magnetic field
generating device configured to carry and convey a developer,
including toner and carrier, on its surface;
a developer regulating member configured to regulate a quantity of
the developer carried and conveyed by the developer bearing member
toward a developing area;
a developer accommodating unit configured to accommodate the
developer regulated to be conveyed toward the developing area by
the developer regulating member; and
a toner accommodating unit including a toner supplying opening
opposing a surface of the developer bearing member at a position
adjacent to and upstream of the developer accommodating unit in a
developer conveying direction, wherein the toner in the toner
accommodating unit is taken into the developer on the developer
bearing member based on a toner density of the developer on the
developer bearing member by a movement of the developer with a
conveyance of the developer on the developer bearing member;
and
a flexible plate-like member opposing, without contacting, a
surface of the developer bearing member in the developer
accommodating unit at a position adjacent to the toner
accommodating unit so as to contact a part of the developer carried
and conveyed by the developer bearing member, where the toner is
taken into the developer from the toner accommodating unit.
31. A developing device according to claim 30, further comprising a
second developer regulating member located between the toner
supplying opening of the toner accommodating unit and the developer
accommodating unit and configured to regulate a quantity of the
developer carried and conveyed by the developer bearing member
toward the developer accommodating unit from the toner supplying
opening of the toner accommodating unit.
32. A developing device according to claim 30, wherein
a length of a free end part of the flexible plate-like member from
a fixed supporting part thereof is longer than a length of a
virtual straight line extending from the fixed supporting part of
the flexible plate-like member to a position on a surface of the
developer bearing member.
33. A developing device according to claim 31, wherein
a thickness of the flexible plate-like member is such that the
flexible plate-like member is bent by a pressing force received
from the developer carried and conveyed by the developer bearing
member.
34. A developing device according to claim 32, wherein
the length of the free end part of the flexible plate-like member
from the fixed supporting part thereof is such that the free end
part of the flexible plate-like member is bent by a pressing force
received from the developer carried and conveyed by the developer
bearing member.
35. A developing device according to claim 30, wherein
a part of the flexible plate-like member opposing a surface of the
developer bearing member is rolled up.
36. An image forming apparatus, comprising:
a latent image bearing member;
a latent image forming device configured to form a latent image on
the latent image bearing member;
a developing device configured to develop the latent image on the
latent image bearing member to form a toner image; and
a transfer device configured to transfer the toner image onto a
transfer sheet,
the developing device comprising:
a developer bearing member including an internal magnetic field
generating device and configured to carry and convey a developer,
including toner and carrier, on its surface;
a developer regulating member configured to regulate a quantity of
the developer carried and conveyed by the developer bearing member
toward a developing area;
a developer accommodating unit configured to accommodate the
developer regulated to be conveyed toward the developing area by
the developer regulating member; and
a toner accommodating unit including a toner supplying opening
opposing a surface of the developer bearing member at a position
adjacent to and upstream of the developer accommodating unit in a
developer conveying direction, wherein the toner in the toner
accommodating unit is taken into the developer on the developer
bearing member based on a toner density of the developer on the
developer bearing member by a movement of the developer with a
conveyance of the developer on the developer bearing member;
and
a peeling off member opposing, without contacting, a surface of the
developer bearing member in the developer accommodating unit and
configured to peel off an upper layer part of the developer carried
and conveyed by the developer bearing member.
37. An image forming apparatus according to claim 36, the
developing device further comprising:
a second developer regulating member located between the toner
supplying opening of the toner accommodating unit and the developer
accommodating unit and configured to regulate a quantity of the
developer carried and conveyed by the developer bearing member
toward the developer accommodating unit from the toner supplying
opening of the toner accommodating unit, and
wherein a gap between the second regulating member and a surface of
the developer nearing member is set such that an amount of the
developer regulated by the second developer regulating member
increases as the toner density of the developer on the developer
bearing member increases.
38. An image forming apparatus according to claim 37, wherein a
relation 0<Gh<Gd2 is satisfied, wherein Gh is a gap between
the peeling off member and the surface of the developer bearing
member and Gd2 is the gap between the second developer regulating
member and the surface of the developer member.
39. An image forming apparatus according to claim 37, wherein the
magnetic force generating device is configured so as not to have a
magnetic pole between a position opposing the peeling off member
and a position opposing the second developer regulating member.
40. An image forming apparatus according to claim 39, wherein a
magnetic flux density on a surface of the developer bearing member
from the position opposing the second developer regulating member
and the position opposing the peeling off member is such that the
developer is carried on the surface of the developer bearing member
by a magnetic force.
41. An image forming apparatus according to claim 36, wherein:
the peeling off roller comprises a roller-like shaped rotating
member; and
the developing device further comprises a rotation driving device
configured to drive the peeling off member to rotate such that a
surface of the peeling off member moves, at a position opposing the
developer bearing member, in a direction opposite a direction in
which the surface of the developer bearing member moves.
42. An image forming apparatus according to claim 41, wherein the
peeling off member includes a magnetic member.
43. An image forming apparatus according to claim 42, wherein:
the peeling off member is supported at its both ends in a direction
perpendicular to a direction of conveying the developer on the
developer bearing member; and
a diameter of the peeling off member at its center in the direction
perpendicular to the developer conveying direction is smaller than
diameters at both ends of the peeling off member.
44. An image forming apparatus according to claim 36, wherein:
the peeling off member extends in a direction perpendicular to a
direction of conveying the developer on the developer bearing
member and includes a magnetic member; and
the developing device further comprises a rotation driving device
configured to drive the peeling off member to rotate such that a
surface of the peeling off member moves, at a position opposing the
developer bearing member, in a direction opposite a direction in
which the surface of the developer bearing member moves.
45. An image forming apparatus according to claim 36, wherein:
the peeling off member extends in a direction perpendicular to a
direction of conveying the developer on the developer bearing
member and a magnetic pole is magnetized at a surface thereof;
and
the developing device further comprises a rotation driving device
configured to drive the peeling off member to rotate such that a
surface of the peeling off member moves, at a position opposing the
developer bearing member, in a direction opposite a direction in
which the surface of the developer bearing member moves.
46. An image forming apparatus according to claim 45, wherein:
the peeling off member comprises a roller-like shaped rotating
member; and
a plurality of magnetic poles are magnetized at a surface of the
peeling off member.
47. An image forming apparatus according to claim 46, wherein the
plurality of magnetic poles are magnetized such that S and N poles
are alternately arranged.
48. An image forming apparatus according to claim 47, wherein each
of the plurality of poles is magnetized linearly in an extending
direction of a rotation axis of the peeling off member.
49. An image forming apparatus according to claim 46, wherein the
plurality of magnetic poles are magnetized such that a plurality of
N and S poles alternately arranged in the extending direction of
the peeling off member are arranged in a circumferential direction
of the peeling off roller.
50. An image forming apparatus according to claim 41, wherein the
rotation driving device drives the peeling off member to rotate at
varied speeds.
51. An image forming apparatus according to claim 50, further
comprising:
a control device configured to control the rotation driving device
according to an image ratio of an image for printing.
52. An image forming apparatus according to claim 50, further
comprising:
a temperature measuring device configured to measure a temperature
inside of the developing device; and
a control device configured to control the rotation driving device
according to a result of measuring the temperature with the
temperature measuring device.
53. An image forming apparatus according to claim 50, further
comprising:
a humidity measuring device configured to measure a humidity inside
of the developing device; and
a control device configured to control the rotation driving device
according to a result of measuring the humidity with the humidity
measuring device.
54. A developing device according to claim 50, wherein
the rotation driving device is controlled such that a relation
0.5<T/S<1.5 is satisfied, wherein S(mm/s) is a linear speed
of the developer bearing member and T(mm/s) is a linear speed of
the peeling off member.
55. An image forming apparatus according to claim 41, wherein a
surface of the peeling off member is coarse.
56. An image forming apparatus according to claim 42, wherein:
the peeling off member comprises a magnetic member; and
the peeling off member opposes a peak position of a magnetic flux
density distribution in a direction of a normal line on a surface
of the developer bearing member.
57. An image forming apparatus according to claim 56, wherein a
magnetic flux density distribution in a direction of a normal line
at a circumferential surface of the peeling off roller opposite a
side thereof opposing the developer bearing member is greater than
5 mT.
58. An image forming apparatus according to claim 56, further
comprising:
a second developer regulating member located between the toner
supplying opening of the toner accommodating unit and the developer
accommodating unit to regulate a quantity of the developer carried
and conveyed by the developer bearing member toward the developer
accommodating unit from the toner supplying opening of the toner
accommodating unit; and
wherein a relation MF2<(2/3)MF1 is satisfied, wherein MF1 is a
magnetic force received by the developer on the developing bearing
member at a position opposing the peeling off roller and MF2 is a
magnetic force received by the developer on the developing bearing
member at a position opposing the second developer regulating
member.
59. An image forming apparatus according to claim 36, wherein:
the peeling off member includes a scooping surface extending in a
direction perpendicular to a direction of conveying the developer
on the developer bearing member configured to scoop an upper layer
of the developer on the developer bearing member to be peeled off
the developer bearing member; and
a scooping angle of the scooping surface of the peeling off member
relative to a tangent line in a direction of conveying the
developer at a surface of the developer bearing member is than 90
degrees.
60. An image forming apparatus according to claim 36, wherein the
peeling off member is a grid-like flat plate.
61. An image forming apparatus, comprising:
a latent image bearing member;
a latent image forming device configured to form a latent image on
the latent image bearing member;
a developing device configured to develop the latent image on the
latent image bearing member to form a toner image; and
a transfer device configured to transfer the toner image onto a
transfer sheet, the developing device comprising:
a developer bearing member including an internal magnetic field
generating device and configured to carry and convey a developer,
including toner and carrier, on its surface;
a developer regulating member configured to regulate a quantity of
the developer carried and conveyed by the developer bearing member
toward a developing area;
a developer accommodating unit configured to accommodate the
developer regulated to be conveyed toward the developing area by
the developer regulating member;
a toner accommodating unit including a toner supplying opening
opposing a surface of the developer bearing member at a position
adjacent to and upstream of the developer accommodating unit in a
developer conveying direction, wherein the toner in the toner
accommodating unit is taken into the developer on the developer
bearing member based on a toner density of the developer on the
developer member by a movement of the developer with a conveyance
of the developer on the developer bearing member;
a developer stirring member opposing, without contacting, a surface
of the developer bearing member in the developer accommodating unit
at a position adjacent to the toner accommodating unit so as to
stir a part of the developer carried and conveyed by the developer
bearing member, where the toner is taken into the developer from
the toner accommodating unit,
wherein the developer stirring member comprises a comb-like member
having comb teeth at one end thereof.
62. An image forming apparatus according to claim 61, the
developing device further comprising a second developer regulating
member located between the toner supplying opening of the toner
accommodating unit and the developer accommodating unit and
configured to regulate a quantity of the developer carried and
conveyed by the developer bearing member toward the developer
accommodating unit from the toner supplying opening of the toner
accommodating unit.
63. An image forming apparatus according to claim 61, wherein a
relation 0<Gk<Gd is satisfied, wherein Gd is a gap between a
surface of the developer bearing member and the second developer
regulating member and Gk is a gap between a surface of the
developer bearing member and a tip end of the comb teeth of the
comb-like member.
64. An image forming apparatus according to claim 61, wherein an
interval between tip ends of the comb teeth of the comb-like member
is less than 5 mm.
65. An image forming apparatus, comprising:
a latent image bearing member;
a latent image forming device configured to form a latent image on
the latent image bearing member;
a developing device configured to develop the latent image on the
latent image bearing member to form a toner image; and
a transfer device configured to transfer the toner image onto a
transfer sheet,
the developing device comprising:
a developer bearing member including an internal magnetic field
generating device and configured to carry and convey a developer,
including toner and carrier, on its surface;
a developer regulating member configured to regulate a quantity of
the developer carried and conveyed by the developer bearing member
toward a developing area;
a developer accommodating unit configured to accommodate the
developer regulated to be conveyed toward the developing area by
the developer regulating member; and
a toner accommodating unit including a toner supplying opening
opposing a surface of the developer bearing member at a position
adjacent to and upstream of the developer accommodating unit in a
developer conveying direction, wherein the toner in the toner
accommodating unit is taken into the developer on the developer
bearing member based on a toner density of the developer on the
developer bearing member by a movement of the developer with a
conveyance of the developer on the developer bearing member;
and
a flexible plate-like member opposing, without contacting, a
surface of the developer bearing member in the developer
accommodating unit at a position adjacent to the toner
accommodating unit so as to contact a part of the developer carried
and conveyed by the developer bearing member, where the toner is
taken into the developer from the toner accommodating unit.
66. An image forming apparatus according to claim 65, the
developing device further comprising a second developer regulating
member located between the toner supplying opening of the toner
accommodating unit and the developer accommodating unit and
configured to regulate a quantity of the developer carried and
conveyed by the developer bearing member toward the developer
accommodating unit from the toner supplying opening of the toner
accommodating unit.
67. An image forming apparatus according to claim 65, wherein a
length of a free end part of the flexible plate-like member from a
fixed supporting part thereof is longer than a length of a virtual
straight line extending from the fixed supporting part of the
flexible plate-like member to a position on a surface of the
developer bearing member the free end part of the flexible
plate-like member contacts.
68. An image forming apparatus according to claim 65, wherein a
thickness of the flexible plate-like member is such that the
flexible plate-like member is bent by a pressing force received
from the developer carried and conveyed by the developer bearing
member.
69. An image forming apparatus according to claim 67, wherein the
length of the free end part of the flexible plate-like member from
the fixed supporting part thereof is such that the free end part of
the flexible plate-like member is bent by a pressing force received
from the developer carried and conveyed by the developer bearing
member.
70. An image forming apparatus according to claim 65, wherein a
part of the flexible plate-like member opposing a surface of the
developer bearing member is rolled up.
71. A developing device, comprising:
developer bearing means, including internal means for generating a
magnetic field, for carrying and conveying a developer, including
toner and carrier, on a surface;
means for regulating a quantity of the developer carried and
conveyed by the developer bearing means toward a developing
area;
means for accommodating the developer regulated to be conveyed
toward the developing area by the developer regulating means;
and
means for accommodating toner, including a toner supplying opening
opposing a surface of the developer bearing means at a position
adjacent to and upstream of the developer accommodating means in a
developer conveying direction, wherein the toner in the toner
accommodating means is taken into the developer on the developer
bearing means based on a toner density of the developer on the
developer bearing means by a movement of the developer with a
conveyance of the developer on the developer bearing means; and
means for peeling off the developer from the developer bearing
means, without contacting a surface of the developer bearing means
in the developer accommodating means to peel off an upper layer
part of the developer carried and conveyed by the developer bearing
means.
72. A developing device, comprising:
developer bearing means including internal means for generating a
magnetic field for carrying and conveying a developer, including
toner and carrier, on a surface;
means for regulating a quantity of the developer carried and
conveyed by the developer bearing means toward a developing
area;
means for accommodating the developer regulated to be conveyed
toward the developing area by the developer regulating means;
and
means for accommodating toner, including a toner supplying opening
opposing a surface of the developer bearing means at a position
adjacent to and upstream of the developer accommodating means in a
developer conveying direction, wherein the toner in the toner
accommodating means is taken into the developer on the developer
bearing means based on a toner density of the developer on the
developer bearing means by a movement of the developer with a
conveyance of the developer on the developer bearing means; and
means for stirring the developer, without contacting a surface of
the developer bearing means, in the developer accommodating means
at a position adjacent to the toner accommodating means so as to
stir a part of the developer carried and conveyed by the developer
bearing means, where the toner is taken into the developer from the
toner accommodating means, and including a comb-like member having
comb teeth at one end thereof.
73. A developing device, comprising:
developer bearing means including internal means for generating a
magnetic field, for carrying and conveying a developer including,
toner and carrier, on a surface;
means for regulating a quantity of the developer carried and
conveyed by the developer bearing means toward a developing
area;
means for accommodating the developer regulated to be conveyed
toward the developing area by the developer regulating means;
and
means for accommodating toner, including a toner supplying opening
opposing a surface of the developer bearing means at a position
adjacent to and upstream of the developer accommodating means in a
developer conveying direction, wherein the toner in the toner
accommodating means is taken into the developer on the developer
bearing means based on a toner density of the developer on the
developer bearing means by a movement of the developer with a
conveyance of the developer on the developer bearing means; and
a flexible plate-like means opposing, without contacting, a surface
of the developer bearing member in the developer accommodating unit
at a position adjacent to the toner accommodating unit for
contacting a part of the developer carried and conveyed by the
developer bearing member, where the toner is taken into the
developer from the toner accommodating unit.
74. An image forming apparatus, comprising:
means for bearing a latent image;
means for forming the latent image on the latent image bearing
means;
means for developing the latent image on the latent image bearing
means to form a toner image; and
means for transferring the toner image onto a transfer sheet,
the developing means comprising:
developer bearing means including internal means for generating a
magnetic field, for carrying and conveying a developer, including
toner and carrier, on a surface;
means for regulating a quantity of the developer carried and
conveyed by the developer bearing means toward a developing
area;
means for accommodating the developer regulated to be conveyed
toward the developing area by the developer regulating means;
and
means for accommodating toner, including a toner supplying opening
opposing a surface of the developer bearing means at a position
adjacent to and upstream of the developer accommodating means in a
developer conveying direction, wherein the toner in the toner
accommodating means is taken into the developer on the developer
bearing means based on a toner density of the developer on the
developer bearing means by a movement of the developer with a
conveyance of the developer on the developer bearing means; and
means for peeling off the developer from the developer bearing
means, without contacting a surface of the developer bearing means
in the developer accommodating means to peel off an upper layer
part of the developer carried and conveyed by the developer bearing
means.
75. An image forming apparatus, comprising:
means for bearing a latent image;
means for forming the latent image on the latent image bearing
means;
means for developing the latent image on the latent image bearing
means to form a toner image; and
means for transferring the toner image onto a transfer sheet, the
developing means comprising:
developer bearing means including internal means for generating a
magnetic field, for carrying and conveying a developer including,
toner and carrier, on a surface;
means for regulating a quantity of the developer carried and
conveyed by the developer bearing means toward a developing
area;
means for accommodating the developer regulated to be conveyed
toward the developing area by the developer regulating means;
and
means for accommodating toner, including a toner supplying opening
opposing a surface of the developer bearing means at a position
adjacent to and upstream of the developer accommodating means in a
developer conveying direction, wherein the toner in the toner
accommodating means is taken into the developer on the developer
bearing means based on a toner density of the developer on the
developer bearing means by a movement of the developer with a
conveyance of the developer on the developer bearing means; and
means for stirring the developer, without contacting a surface of
the developer bearing means in the developer accommodating means at
a position adjacent to the toner accommodating means so as to stir
a part of the developer carried and conveyed by the developer
bearing means, where the toner is taken into the developer from the
toner accommodating means, and including a comb-like member having
comb teeth at one end thereof.
76. An image forming apparatus, comprising:
means for bearing a latent image;
means for forming the latent image on the latent image bearing
means;
means for developing the latent image on the latent image bearing
means to form a toner image; and
means for transferring the toner image onto a transfer sheet,
the developing means comprising:
a developer bearing means including internal means for generating a
magnetic field, for carrying and conveying a developer, including
toner and carrier, on a surface;
means for regulating a quantity of the developer carried and
conveyed by the developer bearing means toward a developing
area;
means for accommodating the developer regulated to be conveyed
toward the developing area by the developer regulating means;
and
means for accommodating toner, including a toner supplying opening
opposing a surface of the developer bearing means at a position
adjacent to and upstream of the developer accommodating means in a
developer conveying direction, wherein the toner in the toner
accommodating means is taken into the developer on the developer
bearing means based on a toner density of the developer on the
developer bearing means by a movement of the developer with a
conveyance of the developer on the developer bearing means; and
a flexible plate-like means opposing, without contacting, a surface
of the developer bearing member in the developer accommodating unit
at a position adjacent to the toner accommodating unit so as to
contact a part of the developer carried and conveyed by the
developer bearing member, where the toner is taken into the
developer from the toner accommodating unit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image forming apparatuses such as
copying machines, printers, facsimiles, etc. and a developing
device for use in such image forming apparatuses. The present
invention more particularly relates to a developing device and an
image forming apparatus using the developing device that uses a two
component developer including a toner and a magnetic carrier and
that includes a self toner density control device to control the
toner density of the developer on a developer bearing member so as
to be within a fixed range without using a complex toner
replenishing device.
2. Discussion of the Background
An example of a developing device that controls the density of
toner in the developer on a developer bearing member without using
a complex toner replenishing device is one in which the quantity of
developer carried on and conveyed by a developer bearing member,
that has an internally disposed magnetic field generating device,
is regulated by a developer regulating member. The developer
scraped off by the developer regulating member is put in a
developer accommodating unit, and toner accommodated in a toner
accommodating unit is supplied to the developer carried on the
developer bearing member through a toner supplying opening, which
is adjacent to the developer accommodating unit upstream in a
developer conveying direction and which opposes a surface of the
developer bearing member (see e.g. Japanese Laid-open Patent
publication No. 9-22178). In this developing device, the toner
contacting the developer carried on and conveyed by the developer
bearing member at the toner supplying opening is taken into the
conveyed developer at the interface between the conveyed developer
and the developer in the developer accommodating unit. Once the
toner density of the developer on the developer bearing member
reaches a certain level, the volume of the developer accommodated
in the developer accommodating unit starts to swell and thereby the
developer in the developer accommodating unit extends so as to
cover the toner supplying opening. As a result, the toner is
stopped from being taken into the developer on the developer
bearing member from the toner accommodating unit at the toner
supplying opening. Thus, the toner density of the developer on the
developer bearing member is controlled to be within a fixed
range.
Also, a developing device is known in which a second developer
regulating member is provided between the developer accommodating
unit and the toner supplying opening of the toner accommodating
unit so as to have a predetermined gap relative to a surface of a
developer bearing member (see e.g. Japanese Laid-open Patent No.
9-197833). In this developing device, as the toner density of the
developer on the developer bearing member increases, the thickness
of a developer layer on the developer bearing member increases, and
the increased portion of the developer layer is regulated by the
second developer regulating member to pass the second developer
regulating member. The developer thus regulated by the second
developer regulating member covers the toner supplying opening
located adjacent to and upstream of the second developer regulating
member in the developer conveying direction, and thereby the toner
is stopped from being taken into the developer being carried and
conveyed by the developer bearing member. As a result, the toner
density of the developer on the developer bearing member is
controlled to be within a fixed range.
Such developing devices as noted above that control the toner
density of the developer on a developer bearing member to be within
a certain range (such a control is hereinafter referred to as a
self toner density control) have an advantage in that a toner
supplying unit can be simplified, because a toner density sensor is
not required, and further a stirring device such as a paddle screw
for stirring the developer can be eliminated. In addition, compared
to a two component developing method, less magnetic carrier is
required. Therefore, torque of the apparatus can be greatly
reduced. From these points, the apparatus can be made compact and
the cost of the apparatus reduced. Furthermore, because the toner
in the toner accommodating unit can be directly supplied to the
developer on the developer bearing member passing a developing
area, the toner is promptly supplied to a part of the developer on
the developer bearing member, where the toner density has been
reduced by passing through the developing area. Accordingly, the
developing devices can develop a solid image without decreasing the
image density.
However, in such developing devices with a self toner density
control capability, background soiling and decrease of image
density occasionally occur with the lapse of time. Also, uneven
image density sometimes occurs in a widthwise direction of an
image, which direction is perpendicular to the direction in which
the developer on the developer bearing member is conveyed
(hereinafter referred to as the image width direction). The
inventors of the present invention have analyzed the causes of the
decrease in the image quality, and have found that the followings
are some of the possible causes.
First, background soiling and decrease of image density with the
lapse of time might be caused by an early deterioration of
developer due to insufficient replacement of the developer on a
developer bearing member with the developer in a developer
accommodating unit. That is, if the developer carried on the
developer bearing member is conveyed without being peeled off the
developer bearing member at all, the developer on the developer
bearing member is hardly replaced with the developer in the
developer accommodating unit. If such replacement of the developer
is not made, stress to the magnetic carrier in the developer
carried on the developer bearing member is increased, which may
lead to a deterioration of the magnetic carrier earlier than the
magnetic carrier in the developer accommodated in the developer
accommodating unit. If the magnetic carrier on the developer
bearing member deteriorates earlier than the magnetic carrier in
the developer in the developer accommodating unit, even when the
developer as a whole in the developing device is not deteriorated
so much, the charging capability of the magnetic carrier on the
developer bearing member, that acts on a formation of a toner
image, might be decreased. The decrease of the charging capability
of the developer on the developer bearing member causes background
soiling or decrease in the image density, thereby decreasing the
image quality. Accordingly, the developer is forced to be replaced
earlier than desired.
If a replacement of the developer on a developer bearing member
with the developer in a developer accommodating unit is not
sufficiently performed, inferior toner charging may also result.
Namely, when such a replacement of the developer is not made, the
toner in an amount corresponding to a consumed amount of the toner
on the developer bearing member, which has been supplied onto the
developer bearing member, must be mixed thereupon with the
developer so as to be charged. However, when the surface moving
speed of the developer bearing member is relatively fast (e.g.,
several hundred rpm when the developer bearing member is a roller),
the toner can not be sufficiently charged in time for development,
thereby causing an inferior charging of the toner. In particular,
when much toner has been consumed at some parts of the developer
bearing member, decrease of image density remarkably appears in
such parts compared to other parts, thereby leading to a decrease
of the image quality.
Secondly, uneven image density in the width direction of the
developer bearing member (i.e., in the image width direction) might
be caused by uneven toner charging in the width direction of the
developer bearing member. When new toner is supplied to a part of
the developer where toner has been consumed, supplying of the new
toner might be delayed or the supplying quantity of the new toner
might be varied. Such a delay in supplying new toner or an uneven
new toner supplying amount causes a decrease in the toner density
of the developer at the corresponding parts of the developer, and
as a result the toner charging amount increases. In particular,
when an image consuming a large amount of toner, such as one having
a solid part, is formed, supplying of a sufficient amount of toner
to a part of the developer, where the large amount of toner has
been consumed, can not be made in time for a next development, and
the next development might be performed with developer with
decreased toner density at that part of the developer. Also,
because toner is rather rapidly taken into a part of the developer
where a large amount of toner has been consumed, extra toner may be
unnecessarily taken into the part of the developer, leading to a
development of a subsequent image with unnecessarily high toner
density at that part of the developer.
Further, because toner is not consumed at non-image parts of an
image, toner should not be taken into such parts of the developer
corresponding to the non-image parts of the image. However, a small
amount of the toner might be also taken into such parts of the
developer corresponding to the non-image parts of the image,
thereby causing an increase of the toner density and resulting in a
decrease of the toner charging.
Thus, if uneven toner density or uneven toner charging occurs in
the developer on the developer bearing member in the width
direction of the developer bearing member, uneven image density is
caused in the width direction of the developer bearing member such
that a part of the image corresponding to a part of the developer
where the toner density is low and the toner charging is high is
relatively faint, forming a white strip, and a non-image part
corresponding to a part of the developer where the toner density is
high and the toner charging is low is relatively dark.
In addition, uneven image density in the width direction of the
developer bearing member might be also caused by a variation in the
dimension or position of a toner supplying opening of a toner
accommodating unit in the width direction of the developer bearing
member or by a variation of a magnetic force of a magnetic roller,
that is provided inside of the developer bearing member as a
magnetic force generating device, in the width direction of the
developer bearing member.
Furthermore, the inventors of the present invention have also found
that uneven image density in the width direction of a developer
bearing member might be also caused by surface roughness of a part
of a second developer regulating member opposing the developer
bearing member or by an insufficient pressing force of an agitator
provided in a toner accommodating unit for pressing the toner to be
conveyed. Specifically, the surface roughness of the part of the
second developer regulating member opposing the developer bearing
member affects the quantity of toner to be taken into the
developer. If the surface roughness is uneven in the width
direction of the developer bearing member, the quantity of toner to
be taken into the developer becomes uneven in the width direction
of the developer bearing member, and thereby uneven image density
is caused in the width direction of the developer bearing member.
The toner pressing force of the agitator in the toner accommodating
unit also affects the quantity of toner to be taken into the
developer. If the toner pressing force of the agitator is uneven in
the width direction of the developer bearing member, and when the
toner pressing force is not sufficient to convey toner to a part of
the developer where a large amount of toner is necessary for
forming, for example, a solid image, the toner cannot be
sufficiently taken into such a part of the developer, thereby
causing uneven image density in the width direction of the
developer bearing member.
The inventor of the present invention has proposed a developing
device having a second developer regulating member, in which a
developer peeling off member for peeling off the developer on a
developer bearing member and a developer stirring member for
stirring the developer are provided in a developer accommodating
unit for preventing the above-discussed uneven image density from
occurring (see e.g. Japanese Laid-open Patent Publication No.
10-232540). In that developing device, all of the developer carried
and conveyed by the developer bearing member inside the developer
accommodating unit is once peeled off by the developer peeling off
member and the peeled off developer is stirred by the stirring
member. According to a result of an experiment recently made by the
inventors of the present invention with the above developing
device, it has been found that the self toner density control is
not stable enough and that in the worst case the self toner density
control does not appropriately function. Specifically, because all
of the developer on the developer bearing member is peeled off in
the developer accommodating unit, the peeled off developer is
accommodated in the developer accommodating unit one after another
until the space in the developer accommodating unit is filled with
the peeled off developer. Therefore, when the toner density is
increased, it is hard to suppress a movement of the developer on
the developer bearing member at the upstream side of the developer
peeling off member in the developer conveying direction, such that
a developer accumulated portion is not formed as desired upstream
of the second developer regulating member in the developer
conveying direction.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-discussed
and other problems and addresses the above-discussed and other
problems.
Preferred embodiments of the present invention provide a novel
developing device and image forming device using the developing
device, which prevent background soiling and decrease of image
density due to a lapse of time while maintaining a stable self
toner density control, and which at the same time perform a
satisfactory development without causing uneven image density in
the width direction of a developer bearing member, which is
perpendicular to a direction in which the developer on the
developer bearing member is conveyed.
Preferred embodiments of the present invention also provide a novel
developing device and image forming apparatus using the developing
device, which performs a satisfactory development without causing
uneven image density in the width direction of the developer
bearing member while keeping a stable self toner density
control.
According to a preferred embodiment of the present invention, a
developing device includes a developer bearing member which
includes an internal magnetic field generating device and which is
configured such that a surface thereof moves so as to carry and
convey a developer including toner and carrier. A developer
regulating member is configured to regulate a quantity of the
developer carried and conveyed by the developer bearing member
toward a developing area, and a developer accommodating unit is
configured to accommodate the developer regulated to be conveyed
toward the developing area by the developer regulating member. A
toner accommodating unit is configured to have a toner supplying
opening opposing a surface of the developer bearing member at a
position adjacent to and upstream of the developer accommodating
unit in a developer conveying direction. The toner in the toner
accommodating unit is taken into the developer on the developer
bearing member based on a toner density of the developer on the
developer bearing member by a movement of the developer with a
conveyance of the developer on the developer bearing member.
According to the preferred embodiment, the developing device
further includes a peeling off member that opposes, without
contacting, a surface of the developer bearing member in the
developer accommodating unit so as to peel off an upper layer part
of the developer carried and conveyed by the developer bearing
member.
In the developing device of the above preferred embodiment, an
upper layer part of the developer on the developer bearing member,
which is conveyed to a position opposing the developer
accommodating unit, is peeled off by the peeling off member in the
developer accommodating unit. The developer thus peeled off by the
peeling off member is mixed with the developer accommodated in the
developer accommodating part. By this mixing of the developer, the
toner taken in the developer is stirred and distributed, and at the
same time the charging of the toner is accelerated, and thereby the
distribution and the charging amount of the toner in the developer
on the developer bearing member are made uniform. A part of the
developer thus mixed in the developer accommodating unit is carried
by the developing sleeve at the downstream side of the peeling off
member in the developer conveying direction together with the
developer carried by the developer bearing member without having
been peeled off by the peeling off member. The developer on the
developer bearing member is regulated by the developer regulating
member so as to have a predetermined layer thickness and is then
used for development. Because only the upper layer part of the
developer on the developer bearing member is peeled off, the effect
of peeling off the developer relative to the conveyance of the
developer on the developer bearing member is suppressed and thereby
the self toner density control is stably performed without being
deteriorated.
According to another preferred embodiment of the present invention,
the developing device includes a developer stirring member which
opposes, without contacting, a surface of the developer bearing
member in the developer accommodating unit at a position adjacent
to the toner accommodating unit so as to stir a part of the
developer carried and conveyed by the developer bearing member,
where the toner has been taken into the developer from the toner
accommodating unit.
In the developing device of the above another preferred embodiment
of the present invention, the upper layer part of the developer on
the developer bearing member entered into the developer
accommodating part is peeled off by the developer stirring member
which opposes, without contacting, a surface of the developer
bearing member in the developer accommodating unit at the position
adjacent to the toner accommodating part. By this stirring of the
developer, the mixing of the developer on the developer bearing
member and that accommodated in the developer accommodating unit is
performed. Further, by this stirring of the developer, the toner
which has been taken in the upper layer part of the developer on
the developer bearing member is stirred and mixed with the
developer such that the toner density of the developer is made
uniform. Thus, the developer in which the toner density is made
uniform is carried by the developer bearing member and conveyed to
a developing area so as to be used for development.
According to still another preferred embodiment of the present
invention, the developing device includes a flexible plate-like
member which opposes, without contacting, a surface of the
developer bearing member in the developer accommodating unit at a
position adjacent to the toner accommodating unit so as to contact
a part of the developer carried and conveyed by the developer
bearing member, where the toner has been taken into the developer
from the toner accommodating unit.
In the developing device according to the above another still
preferred embodiment, a flexible plate-like member opposing a
surface of the developer bearing member at a position adjacent to
the toner accommodating part in the developer accommodating unit
contacts the supplied toner existing on the upper layer part of the
developer on the developer bearing member entered into the
developer accommodating part. When the supplied toner contacts the
flexible plate-like member, the flexible plate-like member is bent
or restored by a pressure force of the toner attempting to pass the
flexible plate-like member, thereby preventing the excessive toner
existing on the upper layer part of the developer on the developer
bearing member from being conveyed to an area at the downstream
side of the flexible plate-like member in the developer conveying
direction together with the developer on the developer bearing
member. Further, because of the flexible plate-like member, the
supplied toner existing on the upper layer part of the developer on
the developer bearing member is uniformly distributed in a width
direction of the developer bearing member, which is perpendicular
to the developer conveying direction.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the present invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in conjunction with
accompanying drawings, wherein:
FIG. 1 is a schematic drawing illustrating a laser printer as an
example of an electrophotographic image forming apparatus to which
a developing device according to an embodiment of the present
invention is applied;
FIG. 2 is a schematic drawing illustrating an exemplary overall
construction of the developing device;
FIG. 3 is an enlarged view of a main part of the developing
device;
FIG. 4 is a schematic drawing for explaining a positional
relationship among a developing sleeve, a peeling off roller, and a
pre-doctor of the developing device;
FIG. 5 is a side view of the peeling off roller;
FIGS. 6(a) and 6(b) are schematic drawings for explaining a self
toner density control mechanism in the developing device;
FIG. 7 is an exemplary block diagram of a control part of the laser
printer;
FIG. 8 is a graph explaining a relation between temperature and a
coagulation degree of toner;
FIG. 9 is a graph explaining a relation between humidity and a
coagulation degree of toner;
FIG. 10 is an enlarged view of a main part of the developing device
including a peeling off member having a scooping surface for
scooping the developer on the developing sleeve so as to be peeled
off the developing sleeve;
FIG. 11 is a diagram illustrating a test chart used for an
experiment, in which black stripes are formed at intervals in a
width direction of the chart;
FIG. 12 is a front view illustrating an exemplary construction of a
printer according to another embodiment of the present
invention;
FIG. 13 is a cross-section of a developing device of the
printer;
FIG. 14 is a cross-section of the developing device in which a
magnetic roller is used for the peeling off roller;
FIG. 15 is another cross-section of the developing device in which
another exemplary magnetic roller is used for the peeling off
roller;
FIG. 16 is a perspective view of the another exemplary magnetic
roller;
FIGS. 17(a)-17(c) are diagrams illustrating peeling off rollers in
which N and S poles are alternately magnetized in the axial
direction of the peeling off rollers;
FIGS. 18(a)-18(e) are diagrams illustrating half-tone images formed
on sheets, respectively having residual black stripes of different
density;
FIG. 19 is a schematic drawing illustrating a developing device
according to still another embodiment of the present invention;
FIG. 20 is a perspective view of a peeling off member used in the
developing device of FIG. 19;
FIG. 21 is a perspective view of another peeling off member of the
developing device;
FIG. 22 is a schematic drawing indicating intervals of relevant
parts of the developing device;
FIG. 23 is a schematic drawing illustrating a developing device
according to still another embodiment of the present invention;
FIG. 24 is a schematic drawing indicating an arrangement position
of a stirring comb member in the developing device;
FIG. 25 is a perspective view of the stirring comb member;
FIG. 26 is a schematic drawing illustrating a developing device
according to still another embodiment of the present invention;
FIG. 27 is a partly enlarged schematic drawing illustrating a
developer accommodating part and a toner take-in part of the
developing device of FIG. 26, including a sheet member;
FIG. 28 is an enlarged schematic drawing illustrating the developer
accommodating part and the toner take-in part of the developing
device, in which another example of the sheet member is
included;
FIG. 29 is an enlarged schematic drawing illustrating the developer
accommodating part and the toner take-in part of the developing
device, in which another example of the sheet member is
included;
FIG. 30 is an enlarged schematic drawing illustrating the developer
accommodating part and the toner take-in part of the developing
device, in which another example of the sheet member is included;
and
FIG. 31 is an enlarged schematic drawing illustrating the developer
accommodating part and the toner take-in part of the developing
device, in which another example of the sheet member is
included.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like reference numerals
designate identical or corresponding parts throughout the several
views, preferred embodiments of the present invention are
described.
FIG. 1 illustrates a laser printer (hereinafter referred to as a
printer) as an example of an electrophotographic image forming
apparatus in which a developing device according to an embodiment
of the present invention can be applied.
A photoconductive drum 1 as a latent image bearing member is
rotated in the direction indicated by arrow A in FIG. 1, and is
uniformly charged, while being rotated, by a charging roller 50
contacting a surface of the photoconductive drum 1. The surface of
the photoconductive drum 1 is scanned and exposed by a light
according to image information with an optical writing unit 51,
thereby forming a latent image thereupon. In this embodiment, a
charging roller 50 and the optical writing unit 51 are used for a
latent image forming device. However, any other types of charging
devices and writing units can be used for the latent image forming
device. The latent image formed on the photoconductive drum 1 is
developed by a later described developing device 2 so as to form a
toner image on the photoconductive drum 1. The toner image formed
on the photoconductive drum 1 is transferred to a sheet 52 as a
transfer member by a transfer device having a transfer roller 53.
The sheet 52 is conveyed from a sheet feeding cassette 54 via a
feeding roller 55 and a registration roller pair 56. The sheet 52
after completion of the transfer passes a fixing unit 57, where the
toner image is fixed to the sheet 52, and the sheet 52 is then
discharged out of the apparatus. Residual toner on the
photoconductive drum 1 is removed from the drum 1 by a cleaning
unit 58, and further, residual charge on the photoconductive drum i
is removed by a discharging lamp 59.
FIG. 2 illustrates an exemplary overall construction of the
developing device 2, and FIG. 3 illustrates a main part of the
developing device 2.
The developing device 2 is arranged beside the photoconductive drum
1, and includes a developing sleeve 4 of non-magnetic material as a
developer bearing member to carry on its surface a two-component
developer 3 (hereinafter referred to as a developer) including a
toner 3a and a magnetic carrier (hereinafter simply referred to as
a carrier). The developing sleeve 4 is disposed so as to be partly
exposed through an opening of a casing 2a, that is formed at the
side of the photoconductive drum 1. The developing sleeve 4 is
configured so as to be driven to be rotated by a driving device
(not shown) in a direction indicated by arrow B to convey the
developer 3 downward in a developing area opposing the
photoconductive drum 1. A magnetic roller 5 including a series of
fixed magnets is provided inside the developing sleeve 4 as a
magnetic field generating device.
The developing device further includes a doctor 6 as a developer
regulating member for regulating the quantity of the developer
carried and conveyed by the developing sleeve 4 toward the
developing area, a developer accommodating case 7 configured so as
to form a developer accommodating part S to accommodate the
developer 3 between a surface of the developing sleeve 4 and the
doctor blade 6 upstream of the doctor blade 6 in a direction in
which the developer 3 is conveyed, and a toner hopper 8 as a toner
accommodating part. The toner hopper 8 includes a toner supplying
opening 8a opposing a surface of the developing sleeve 4 at a
position adjacent to and upstream of the developer accommodating
part S in the direction in which the developer 3 on the developer
sleeve 4 is conveyed. Inside the toner hopper 8, a toner agitator 9
as a toner stirring member is arranged so as to be driven in a
clockwise direction indicated by arrow C to stir and convey the
toner 3a toward the toner supplying opening 8a.
An end part (eaves part) of the developer accommodating case 7 in
close proximity to the developing sleeve 4 is used as a pre-doctor
blade 7a as a second developer regulating member that regulates the
quantity of the developer, to which the toner 3a has been supplied
from the toner hopper 8 and which attempts to move toward the
developer accommodating part S. The developer regulated by the
doctor 6 to move to the developing area is also accommodated in the
developer accommodating part S.
A plurality of magnetic poles are formed at a surface part of the
magnetic roller 5 so as to extend in an axial direction of the
magnetic roller 5. Specifically, a primary pole N1 is disposed in a
position opposing the developing area, and a secondary pole S2 is
disposed between a position opposing the pre-doctor 7a and a
position reaching the developing area so that a magnetic force of
the magnetic field reaches the developer accommodating part S.
Further, as generally practiced in developing devices for an image
forming apparatus, magnetic poles (S and N poles) for carrying the
developer on the developing sleeve 4 to convey the developer are
arranged on a surface of the magnetic roller 5 in an appropriate
manner.
In this embodiment, a fixed magnet member in which a magnet piece
is engaged with and fixed to a substrate member, a so-called block
type magnetic roller, is used for the magnetic roller 5, but any
other type of the magnetic roller 5 can be used. For example, a
so-called integrated plastic magnetic roller of ferrite system,
which is made by magnetizing a plastic magnetic member molded in a
certain shape at the same time the magnetic poles are arranged, can
be used.
The developing device further includes a peeling off roller 11 as a
peeling off member, that opposes, without contacting, a surface of
the developing sleeve 4 in the developer accommodating part S so as
to peel off a part (a surface layer part) of the developer carried
and conveyed by the developing sleeve 4. In this embodiment, a
roller-like rotating member formed by a magnetic member is used for
the peeling off roller 11, but the peeling off roller 11 can be
formed in a cylinder-like shape.
For the peeling off roller 11, a magnetic member such as a SUM
member (sulfur and sulfur-mixed finely-ground steel member), a SUS
member having magnetism, steel, nickel, and so forth, can be used.
Also, a steel core plated with nickel and a stainless member coated
with magnetic material can be used.
The surface of the peeling off roller 11 is preferably roughened by
a sand blasting process and so forth so as to securely carry and
convey the developer peeled off the developing sleeve 4. The
surface roughness of the peeling off roller 11 may be set, for
example, to about 30 .mu.m as defined by JIS (Japan Industrial
Standard). The surface roughness of the peeling off roller 11 may
be appropriately set so that the developer can be conveyed
according to conditions such as the kind of toner and material of
the peeling off roller 11.
The peeling off roller 11 is driven to rotate in the same direction
as the developing sleeve 4 (in the direction indicated by arrow E)
by a driving device (not shown). Because of this rotation, at a
part where the developing sleeve 4 and the peeling off roller 14
oppose each other, the surface of the peeling off roller 14 moves
in an opposite direction relative to a surface moving direction of
the developing sleeve 4. Thereby, the upper layer part of the
developer on the developing sleeve 4 is blocked by the peeling off
roller 11 to be securely peeled off the developing sleeve 4. The
developer thus peeled off is conveyed with the surface movement of
the peeling off roller 11 to separate from the surface of the
developing sleeve 4, and is then mixed with the developer in the
developer accommodating part S.
The magnetic pole S2 of the magnetic roller 5 opposing the
developer accommodating part S is disposed so as not to be located
between the position opposing the peeling off roller 11 and the
position opposing the pre-doctor 7a. In this embodiment, as
illustrated in FIG. 4, the position of the magnetic pole S2 is set
so that the angle .theta. between a line passing through the center
of the magnetic roller 5 and that of the peeling off roller 11 and
a line passing through the center of the magnetic roller 5 and the
magnetic pole S2 is 2-10 degrees.
By thus avoiding the magnetic pole to be disposed between the
position opposing the peeling off roller 11 and the position
opposing the doctor blade 7a, an abnormal flow of the developer in
the developer accommodating part S, such as the one attracted
toward a gap between the pre-doctor blade 7a and the surface of the
developing sleeve 4, is avoided regardless of the toner density of
the developer.
Further, it is preferable to set a gap Gh between the peeling off
roller 11 and the surface of the developing sleeve 4 and a gap Gd2
between the pre-doctor 7a and the surface of the developing sleeve
4 so as to satisfy the relation: 0<Gh<Gd2. By thus setting
the gaps Gh and Gd2, the upper layer part of the developer conveyed
by the developing sleeve 4, into which the toner has been taken
from the toner hopper 8 and which has passed the regulating
position by the pre-doctor blade 7a, securely contacts the peeling
off roller 11 to be peeled off.
When the peeling off roller 11 made of a magnetic member is used, a
magnetic pole is generated at a surface of the peeling off roller
11 by a magnetic force action of the magnetic roller 5 in the
developing sleeve 4, and thereby the developer 3 on the developing
sleeve 4 can be efficiently peeled off. However, because of the
magnetic force acting on the peeling off roller 11, the center part
of the peeling off roller 11 in the axial direction of the peeling
off roller 11 is bent so as to come closer to the developing sleeve
4, and thereby the gap relative to the developing sleeve 4 may
become smaller than desired.
Therefore, when the peeling off roller 11 is configured to be bent
as above, as illustrated in FIG. 5, a diameter D2 at the center
part of the peeling off roller 11 is preferably made smaller than a
diameter D1 of both end parts of the peeling off roller 11. With
the use of the peeling off roller 11 configured as above, the gap
between the peeling off roller 11 and the developing sleeve 4 can
be made substantially uniform over the entire length of the peeling
off roller 11 in the axial direction thereof Accordingly, a uniform
peeling off operation can be performed over the entire part of the
peeling off roller 11 from the center part to the both end parts
thereof.
When the peeling off roller 11 is configured not to be bent, the
peeling off roller 11 can be formed in a straight rod-like shape
having a circular cross-section with a constant diameter over the
entire length thereof in the axial direction.
Now, an exemplary developing operation of the above-described
developing device is described with reference to FIGS. 2 and 3.
The developer 3 on the developing sleeve 4 is conveyed with a
rotation of the developing sleeve 4 in the direction of the arrow
B, and is regulated by the doctor 6 so as to be thinly layered. The
thinly layered developer 3 is conveyed to the developing area
opposing the photoconductive drum 1 rotating in the direction of
the arrow A. In this developing area, toner is supplied to a latent
image formed on the photoconductive drum 1 to visualize the latent
image. The developer on the developing sleeve 4 which has passed
the developing area is further conveyed with the rotation of the
developing sleeve 4 to reach the position opposing the toner
supplying opening 8a. At the toner supplying opening 8a, the toner
3a conveyed thereto by the agitator 9 from the toner hopper 8 halts
there so as to contact the developer on the developing sleeve 4.
The developer on the developing sleeve 4 returns, after taking the
new toner 3a therein to at the toner supplying opening 8a, to the
developer accommodating part S. The developer containing the new
toner 3a is regulated by the doctor 6 and thereby the internal
pressure of the developer increases. The toner is charged by
friction with the carrier in the developer having thus increased
internal pressure. A part of the developer 3 regulated by the
doctor 6 so as not to be conveyed to the developing area is moved
so as to be circulated in the developer accommodating part S.
Next, an exemplary self toner density control operation of the
developing device is described with reference to FIGS. 6(a) and
6(b). In FIGS. 6(a) and 6(b), a two-dot chain line indicates an
interface between developers having different behaviors from each
other.
First, a developer having a predetermined toner density and a
predetermined weight is set in the developing device as an initial
developer, and by driving the developing sleeve 4 and the peeling
off roller 11 so as to rotate, the developer 3 is divided into
three parts, a conveyed developer 3b, an accommodated developer 3c,
and a peeled off developer 3d. The conveyed developer 3b is the
developer that is carried on a surface of the developer sleeve 4 by
a magnetic force and conveyed by being brought around by the
surface of the developing sleeve 4. The accommodated developer 3c
is the developer that is accommodated in the developer
accommodating part S and that moves in the developer accommodating
part S to circulate therein with a movement of the conveyed
developer 3b. The peeled off developer 3d is the developer that is
peeled off the conveyed developer 3b on the developing sleeve 4 and
that moves along a surface of the peeling off roller 11 with a
rotation of the peeling off roller 11.
In the developer accommodating part S, as illustrated in FIG. 6(a),
four developer flows F1, F2, F3, and F4 are generated. The first
developer flow F1 is the flow of the conveyed developer 3b passing
between the developing sleeve 4 and the peeling off roller 11. The
second developer flow F2 is the circulating flow of a part of the
peeled off developer 3d that is peeled off the developing sleeve 4
and that moves along the peeling off roller 11 so as to circulate
in a space between the peeling off roller 11 and the pre-doctor 7a.
The third developer flow F3 is the flow of a part of the peeled off
developer 3d that flows along a surface of the peeling off roller
11 above the peeling off roller 11. The fourth developer flow F4 is
the circulating flow of the accommodated developer 3c that rises
along a back surface of the doctor 6 due to the regulation by the
doctor 6 to circulate in a space between the doctor 6 and the
peeling off roller 11.
Under conditions that the above four developer flows F1-F4 are
generated in the developer accommodating part S, if the toner 3a is
put in the toner hopper 8, the toner 3a is supplied from the toner
supplying opening 8a to the conveyed developer 3b carried by the
developing sleeve 4. The conveyed developer 3b to which the toner
3a has been supplied is conveyed to the developer accommodating
part S together with the supplied toner 3a. While the conveyed
developer 3a is being thus conveyed, the toner 3a which has been
supplied to the conveyed developer 3b slightly shifts toward the
axial center of the developing sleeve 4. After the conveyed
developer 3b to which the toner 3a has been supplied passes the
regulation position of the pre-doctor 7a, the upper layer part
thereof is peeled off by the peeling off roller 11 to become the
peeled off developer 3d. The peeled off developer 3d is conveyed
while being mixed with the accommodated developer 3c, and a part
thereof merges with the above circulating developer flow F2
generated in a vicinity of the pre-doctor 7a. The peeled off
developer 3d being carried and conveyed by the peeling off roller
11 is further conveyed while being mixed with the accommodated
developer 3c, and is then carried again by the developing sleeve 4
downstream of the peeling off roller 11 in the developer conveying
direction to become the conveyed developer 3b. By this mixing of
the peeled off developer 3d with the accommodated developer 3c,
replacement of a part of the peeled off developer 3d with the
accommodated developer 3c, uniform distribution of the toner 3a in
the developer, and toner charging by a frictional charging between
the toner and the carrier are realized.
As the toner density of the developer 3 gradually rises with the
above supply of the toner 3a to the developer 3, the volume of the
developer 3 increases and thereby the layer of t he conveyed
developer 3b on the developing sleeve 4 becomes thick in the area
from the position opposing the toner supplying opening 8a to the
regulation position by the doctor 6.
Because the ratio of the carrier in the conveyed developer 3b on
the developing sleeve 4 decreases as the layer thickness of the
conveyed developer 3b increases, the magnetic force acting on the
conveyed developer 3b decreases, and thereby the moving speed of
the conveyed developer 3b decreases, resulting in further
increasing the layer thickness of the conveyed developer 3b on the
developing sleeve 4 in the above area. This conveyed developer 3b
on the developing sleeve 4 with the increased layer thickness
receives a rather strong braking force in a direction of stopping
the conveyance of the conveyed developer 3b from the peeling off
roller 11, and thereby the moving speed of the conveyed developer
3b being conveyed toward the peeling off position by the peeling
off roller 11 decreases even more.
The upper layer part of the conveyed developer 3b with the layer
thickness having been increased at the position opposing the toner
supplying opening 8a is peeled off by the pre-doctor 7a, and the
peeled off developer starts to halt, as illustrated in FIG. 6(a),
at an upstream side of the pre-doctor 7a in the developer conveying
direction. Hereinafter, the halting developer is referred to as
halting developer 3e. The halting developer 3e circulates along
with a movement of the conveyed developer 3b contacting the halting
developer 3e. The toner 3a supplied to the toner supplying opening
8a is attracted to an exposed part of the conveyed developer 3b,
and is taken into the conveyed developer 3b at a merging point P
where the conveyed developer 3b and the halting developer 3e merge
with each other.
As the toner density of the developer 3 further increases, as
illustrated in FIG. 6(b), the quantity of the halting developer 3e
at the toner supplying opening 8a increases so that the exposed
surface of the conveyed developer 3b contacting the toner 3a is
closed by the halting developer 3e and the merging point P moves up
to an upstream end of the toner supplying opening 8a in the
developer conveying direction, and at the same time, the
circulating and moving speed of the halting developer 3d at the
toner supplying opening 8a decreases, and finally the take-in of
the toner 3a into the developer is completed and the toner density
stops increasing.
The upper layer part of the conveyed developer 3b, into which the
toner 3a has been taken and which has passed the gap between the
pre-doctor 7a and the developing sleeve 4, is peeled off by the
peeling off roller 11. The peeled off developer 3d is conveyed
along a surface of the peeling off roller 11 while being mixed with
the accommodated developer 3c, and a part thereof is again carried
on the developer sleeve 4. The conveyed developer 3b which has
passed the gap between the developer sleeve 4 and the doctor 6 is
conveyed to the developing area opposing the photoconductive drum
1. In the developing area the toner is supplied to a latent image
formed on the photoconductive drum 1 so as to be used for
development of the latent image.
As the toner 3a on the developing sleeve 4 is consumed as a result
of the development of the latent image on the photoconductive drum
1, the toner density of the corresponding part of the conveyed
developer 3b decreases, the conveying force by the developing
sleeve 4 acting on that part of the conveyed developer 3b
increases, and further, the volume of that part of the conveyed
developer 3b decreases. Then, the layer thickness of the conveyed
developer 3b regulated by a tip end of the pre-doctor 7a decreases,
the quantity of the halting developer 3e halting in the vicinity of
the toner supplying opening 8a decreases, and the circulating and
moving speed of the halting developer 3e increases. Thereby, the
conveyed developer 3b conveyed by the developing sleeve 4 is caused
to contact the toner 3a from the toner hopper 8, such that the
toner 3a is again taken into the conveyed developer 3b and the
toner density of the developer 3 is increased as described
above.
As described above, according to a change of the toner density on
the developing sleeve 4, the regulating condition with the
pre-doctor 7a for the conveyed developer 3b on the developing
sleeve 4 changes, and thereby the toner density of a part of the
developer where the toner has been consumed is self controlled so
as to be within a predetermined range. With this self control, the
toner density of the conveyed developer 3b on the developing sleeve
4 is maintained to be constantly in a fixed range. Therefore, a
complicated toner density control mechanism including, for example,
a toner sensor and a toner supplying member, is not necessary.
According to the above-described embodiment of the present
invention, by peeling off a part of the conveyed developer 3b on
the developing sleeve 4 so as to be mixed with the accommodated
developer 3c in the developer accommodating part S, replacement of
the conveyed developer 3b with the accommodated developer 3c is
accelerated, so that early deterioration of the developer 3 due to
a decrease of the charging capability of the carrier in the
developer 3 is prevented. In addition, by mixing the conveyed
developer 3b with the accommodated developer 3c, the toner in the
developer 3 is stirred and distributed such that the toner density
of the developer 3 is made uniform with respect to an image width
direction perpendicular to the developer conveying direction,
making it possible to perform a satisfactory development without
having uneven image density.
Further, according to the above-described embodiment of the present
invention, because the peeling off roller 11 having a circular
shape in its cross-section is used, the gap between the
circumferential surface of the peeling off roller 11 and that of
the developing sleeve 4 does not change even when the peeling
roller 11 rotates. Therefore, an uneven peeling off does not occur.
Accordingly, variation of the toner density and toner charging is
suppressed with respect to the conveyed developer 3b on the
developing sleeve 4 in the developer conveying direction, and
thereby uneven image density in the developer conveying direction
can be avoided. According to an experiment made by the inventors of
the present invention, when a peeling off member having other
shapes than a circular cross-section, for example a crank-like
shape, is used, an uneven peeling off occurs, resulting in having
uneven image density at a pitch corresponding to a rotation pitch
of the crank-like shaped peeling off roller.
According to the above-described embodiment of the present
invention, because the peeling off roller 1 made of a magnetic
member is used, by magnetizing the peeling off roller 11 by the
magnetic roller 5 in the developing sleeve 4, a part of the
conveyed developer 3b carried on and conveyed by the developing
sleeve 4 can be attracted to the peeling off roller 11 by a
magnetic force. Accordingly, peeling the developer off the
developing sleeve 4 and generating the developer flow to force the
peeled off developer to move along a surface of the peeling off
roller 11 as indicated by F3 in FIG. 6(a) can be made rather
remarkably, and thereby mixing and stirring of the peeled off
developer with the developer in the developer accommodating part S
is further efficiently made.
In the above-described embodiment, the peeling off roller 11 may be
configured such that the rotation speed thereof is controlled
according to the ratio of an image part and a non-image part of an
original document for printing or the result of detecting a
temperature and humidity condition in the apparatus.
FIG. 7 is a block diagram of an exemplary control part of the
printer according to the above-described embodiment of the present
invention. Image data received from an outside apparatus 200 such
as a personal computer is processed by an image data processing
part 110. In this image data processing by the image data
processing part 110, data for forming a latent image, that is used
at the latent image forming part, is generated and the image ratio
data of an image for printing is calculated. An engine control part
100 controls each part of the apparatus according to the data sent
from the image data processing part 110. The engine control part
100 includes an engine control CPU 101, a ROM 102, a RAM 103, and
an I/O interface 104. To the engine control part 100, a
photoconductive drum driving part 105, a driving part 106 for the
latent image forming part, a developing device driving part 107,
and a temperature and humidity sensor 108 are connected. The engine
control CPU 101 outputs various instructions to each part of the
apparatus so as to be operated according to a control program read
out from the ROM 102 and in response to an input signal from the
image data processing part 110, while performing various
recognition and determination operations such as ones relating to
operating timings of respective driving parts. The engine control
CPU 101 also controls each part of the apparatus according to
temperature and humidity data obtained by the temperature and
humidity sensor 108.
The engine control part 100 controls the rotation of the peeling
off roller 11 of the developing device 2, for example, according to
the image ratio data of an image for printing. More specifically,
the circumferential moving speed of the peeling off roller 11 is
changed according to a toner consumption, which changes according
to the image ratio, so as to appropriately charge the toner and to
avoid unnecessary mixing of the developer, thereby preventing a
deterioration of the developer.
Further, it has been found in an experiment performed by the
inventors of the present invention that the quantity of the
taken-in toner 3a, the conveying speed of the developer 3, and the
volume of the developer 3 change according to the coagulation
degree of the toner 3a, which changes based on environmental
conditions. The coagulation degree of the toner 3a changes based on
the temperature and humidity, and as illustrated in FIGS. 8 and 9,
the coagulation degree rises under a high temperature condition and
under a high humidity condition as well. A higher coagulation
degree indicates that the toner 3a has become hard.
Accordingly, an ambient temperature near the photoconductive drum 1
is measured by the temperature and humidity sensor 108 provided
inside the apparatus, and when the temperature rises, the linear
speed of the peeling off roller 11 is increased by increasing the
number of rotations of the peeling off roller 11. Thereby, the
developer 3 is sufficiently mixed and stirred, and by which
replacement of the developer 3 with each other and frictionally
charging of the developer 3 are sufficiently accelerated. Also, the
humidity inside the apparatus is measured by the temperature and
humidity sensor 108, and when the humidity rises, by controlling
the driving of the peeling off roller 11 in substantially the same
manner as when the temperature rises, the developer 3 is
sufficiently mixed and stirred, such that replacement of the
developer 3 with each other and frictionally charging of the
developer 3 are sufficiently accelerated.
Further, in this embodiment, as illustrated in FIG. 4, the magnetic
pole S2 in the position opposing the developer accommodating part S
is slightly deviated to the side of the doctor 6; however, the
magnetic pole S2 may be arranged such that the peak position of a
density distribution of a magnetic flux generated by the magnetic
pole S2 in a normal line direction substantially coincides with a
direction leading to the center of the peeling off roller 11. By
this arrangement, the peeling off roller 11 can be most strongly
magnetized and thereby the peeling off and conveying force of the
peeling off roller 11 is most greatly exerted. As a result, in the
developer accommodating part S, the frictional charging of the
developer 3 is effectively made at the gap between the developing
sleeve 4 and the peeling off roller 11.
Further, for effectively circulating the developer 3 along the
circumferential surface of the peeling off roller 11 in the
developer accommodating part S, the magnetic flux distribution in
the normal line direction at a circumferential surface of the
peeling off roller 11 at the side opposite the surface thereof
opposing the developing sleeve 4 may be preferably made to be
greater than 5 mT.
Furthermore, for effectively circulating the developer 3 along the
circumferential surface of the peeling off roller 11 in the
developer accommodating part S, a certain space must be maintained
in the developer accommodating part S so that the developer 3 can
circulate. For maintaining such a space in the developer
accommodating part S, the take-in of the toner 3a must be stopped
while the space remains in the developer accommodating part S. In
this respect, the inventors of the present invention found out
through various experiments that the space can be maintained in the
developer accommodating part S if the following condition (1):
MF2<(2/3)MF1 is satisfied, wherein a magnetic force which is
received by the developer 3 on the developing sleeve 4 at the
position opposing the peeling off roller 11 is MF1 and a magnetic
force which is received by the developer 3 on the developing sleeve
4 at the position opposing the pre-doctor 7a is MF2.
If the above force MF2 becomes relatively large on the developing
sleeve 4, an effect of the breaking force by the peeling off roller
11 does not reach a vicinity of the toner supplying opening 8a. As
a result, the conveying speed of the developer 3 does not decrease
even when the toner density of the developer 3 increases, making it
difficult to increase the thickness of the layer of the developer
3. Accordingly, the taking-in of the toner 3a can not be stopped
until the developer accommodating part S is filled with the
developer 3. Therefore, in this embodiment, as indicated by the
condition (1), the magnetic force MF2 which is received by the
developer 3 at the position opposing the pre-doctor 7a is made
weaker relative to the magnetic force MF1 received by the developer
3 at the position opposing the peeling off roller 11, such that the
effect of the breaking force by the peeling roller 11 reaches the
vicinity of the toner supplying opening 8a. The control of a
waveform of the magnetic force may be appropriately made according
to the position, the magnetism, the shape, and the magnetic force
of a magnet piece arranged at each pole.
Further, in this embodiment, as the peeling off member, the peeling
off roller 11 formed in a rotatable roller-like shape is used;
however, the peeling off member can be differently shaped. For
example, as illustrated in FIG. 10, a peeling off member 10 having
a scooping surface 10a may be provided so as to extend
substantially over the entire longitudinal area of the developer
accommodating space S (the area along an axial direction of the
developing sleeve 4) for scooping the developer 3 on the developing
sleeve 4 so as to be peeled off the developing sleeve 4. The
scooping angle .theta. of the scooping surface 10a of the peeling
off member 10 relative to a tangent line to a surface of the
developing sleeve 4 is preferably greater than 90 degrees so that
the developer 3 is efficiently peeled off without being halted.
Because of this scooping surface 10a of the peeling off member 10,
the upper layer of the conveyed developer 3b being carried and
conveyed by the developing sleeve 4 rotating in a counterclockwise
direction is peeled off and a developer flow indicated by the arrow
D is generated. Due to this flow of the peeled off developer,
mixing and stirring of the developer peeled off the developing
sleeve 4 and the developer in the developer accommodating part S is
accelerated. A part of the developer thus mixed and stirred is
carried on the developing sleeve 4 between the peeling off member
10 and the doctor 6 by a magnetic force.
Now, a result of an experiment made using a concrete example of the
developing device according to the above-described embodiment of
the present invention is described. In the experiment, the
developing device as illustrated in FIG. 2 was used, and 20 prints
were made using a test chart 60 illustrated in FIG. 1. As
illustrated, the test chart 60 includes black stripes which are
formed at intervals so that the toner consumption varies in a
direction perpendicular to a surface moving direction (indicated by
the arrow G in FIG. 11) of the developing sleeve 4, i.e., an image
width direction of the test chart 60. After making 20 prints of the
test chart 60, another 20 prints were made using another test chart
having an even half-tone over the entire surface thereof. The
experiment was made under the conditions of Table 1.
Table 1
Linear speed of the photoconductive drum: 120 mm/sec;
Gap Gp between the developing sleeve and the photoconductive drum:
0.3-0.5 mm;
Gap Gd 1 between the developing sleeve and the doctor: 0.3-0.5
mm;
Gap Gd2 between the developing sleeve and the pre-doctor: 0.5-1.5
mm;
Gap Gh between the developing sleeve and the peeling off roller:
0.2-0.4 mm;
Diameter of the developing sleeve: 16-20 mm;
Linear speed ratio of the developing sleeve and the photoconductive
drum: 1.5-3.0;
Magnetic flux density (in the normal line direction) on the
developing sleeve N1: 93 mT;
Magnetic flux density (in the normal line direction) on the
developing sleeve S1: 75 mT;
Magnetic flux density (in the normal line direction) on the
developing sleeve N2: 60 mT;
Magnetic flux density (in the normal line direction) on the
developing sleeve S2: 53 mT;
Material of the carrier: magnetite or steel;
Particle diameter of the carrier: 40-50 .mu.m;
Volume of the magnetic member in the toner: 15-40 wt %;
Volume of silica in the toner: 0.5-1.0 wt %;
Covered ratio of the toner relative to the carrier: 50-120%;
Q/M: 10-30 .mu.c/g.
For example, using the peeling off roller 11 having the diameter of
7 mm, the gap Gp was set to 0.35 mm, the gap Gd1 to 0.4 mm, the gap
Gd2 to 0.65 mm, and the gap Gh to 0.35 mm. In the experiment made
under the conditions as above, the developer peeled off by the
peeling roller 11 was well mixed and stirred, such that the
developer was made uniform, and thereby a good image without having
uneven image density was obtained. In the above example of the
developing device, the gap Gh between the developing sleeve 4 and
the peeling off roller 11 and the gap Gd2 between the developing
sleeve 4 and the pre-doctor 7a satisfied the relation:
0<Gh<Gd2, and thereby a good stirring capability was obtained
with the peeling off roller 11.
Further, the peeling off roller 11 may be a magnetic member such as
a SUM member, and the center part of the peeling off roller 11 may
be slightly bent so as to come close to the developing sleeve 4 by
0.1 mm under the condition that the magnetic flux density in the
normal line direction on the developing sleeve 4 opposing the
peeling off roller 11 is 56 mT. Therefore, the shape of the peeling
off roller 11 was made, as illustrated in FIG. 5, such that the
center diameter D2 is smaller (6.8 mm) than the diameter D1 at both
ends thereof (7 mm). By thus shaping the peeling off roller 11, the
gap between the peeling off roller 11 and the developing sleeve 4
was kept at about 0.35 mm over the entire axial direction of the
peeling off roller 11, and thereby peeling off of the developer 3
and mixing and stirring of the developer 3 thereafter were
uniformly made over the entire area of the peeling off roller 11
from the center part to the both ends thereof.
On the other hand, when the above test chart having a half-tone
image was printed using a conventional developing device in which
the peeling off member 12 was not used, uneven image density was
observed in the half-tone image. Thus, it has been confirmed that
if the peeling off roller 12 is not provided, when printing a test
chart having black stripes such that the toner consumption changes
in the longitudinal direction of the developing sleeve 4, the toner
density becomes uneven in the longitudinal direction of the
developing sleeve 4, thereby resulting in deteriorating the
produced image.
FIG. 12 is a front view illustrating an exemplary construction of a
printer according to another embodiment of the present invention,
and FIG. 13 is a cross-section illustrating an exemplary
construction of a developing device of the printer. In FIGS. 12 and
13, the parts similar to those of the printer according to the
previous embodiment, illustrated in FIGS. 1 and 2, are denoted by
like references, and the description thereof is omitted because the
function is substantially the same. One-dot-and-dash lines in FIG.
12 and 13 around the developing sleeve 4 respectively denote the
components of a magnetic flux in the normal line direction at a
surface of the developing sleeve 4.
In this embodiment, in contrast to the previous embodiment in which
the peeling off roller 11 made of a magnetic member is used, a
peeling off roller 13 including a magnetic roller, in which the
magnetic pole has been magnetized in advance so as to have a
magnetic force by itself, is used for the peeling off member.
Further, in the developing device, at a bottom part of a casing 2
in a vicinity of a toner supplying opening 8a, a protruded part 2b
having an opposing surface 2c is formed. The opposing surface 2c is
formed so as to have a predetermined length and to be inclined
downward toward the developing sleeve 4. The construction of the
toner hopper 8 is different from that of the previous embodiment,
however, because its relevancy to the invention is very little, the
description thereof is omitted.
FIG. 14 is a cross-section illustrating the developing device in a
more simplified manner than FIG. 13 for highlighting the peeling
off roller 13 including a magnetic roller. In this developing
device, the peeling off roller 13, in which a pair of magnetic
poles (S and N poles) are arranged at a surface thereof so as to
extend along the axial direction thereof, is used, and the peeling
off roller 13 is rotated at a position opposing a magnetic pole 5a
of the developing sleeve 4 as in the previous embodiment. This
peeling off roller 13 can more strongly attract the developer 3,
which is carried and conveyed by the developing sleeve 4, by a
magnetic force. Accordingly, a peeling off of the developer 3 from
the developing sleeve 4 and an enforced flow of the peeled off
developer 3 are more securely performed, and thereby mixing and
stirring of the peeled off developer with the developer in the
developer accommodating part S is more effectively performed.
FIG. 15 is a section view of the developing device including a
peeling off roller 14 having another exemplary magnetic roller. The
peeling off roller 14 includes a plurality of N and S poles
alternately arranged at the circumferential surface thereof. In the
example of the peeling off roller 14 illustrated in FIG. 15, four
pairs of N and S poles are arranged. The peeling off roller 14 is
disposed so as to be rotatable and in a position opposing an S pole
5a of the magnet roller 5 arranged in the developing sleeve 4. When
the peeling off roller 14 rotates and one of the S poles arranged
at its surface thereof comes close to the S pole 5a of the magnet
roller 5, the developer 3 between the peeling off roller 14 and the
developing sleeve 4 receives a force to be expelled therefrom. When
one of the N poles of the peeling off roller 14 comes close to the
S pole 5a, the developer 3 between the peeling off roller 14 and
the developing sleeve 4 receives an attracting force. Thus,
expelling and attracting forces are alternately exerted in a small
space between the developer sleeve 4 and the peeling off roller 14,
and thereby mixing and stirring of the developer in the space is
actively performed so that the toner density is made uniform.
Further, because of the magnetic force of the magnetic poles
alternately magnetized on the peeling off roller 14, a part of the
developer 3 is attracted to the peeling off roller 14 at other
parts than the vicinity of the developing sleeve 4, and thereby the
stirring force is further enhanced. Accordingly, the toner
distribution is more effectively made uniform, and thereby an
abnormal image such as an image having uneven image density is
prevented.
Further, as illustrated in FIG. 16, a plurality of poles 14a, 14b
having substantially the same length as that of the peeling off
roller 14 in the axial direction thereof may be arranged such that
S and N poles are alternately disposed in the circumferential
direction. In this case, when the developer 3 adheres to the
surface of the peeling off roller 14 to form a layer of the
developer 3 threupon, the surface of the layer of the developer 3
is unevenly formed, by which a stirring effect similar to the one
obtained when a member having a uneven surface is used for the
peeling off roller 14 can be obtained.
FIG. 17(a) is a perspective view of another example of the peeling
off roller. A peeling off roller 15 is configured such that a
magnetic pole having a predetermined length in the axial direction
of the peeling off roller 15 is alternately magnetized with a S
pole 15a and a N pole 15b in the axial direction thereof. If the
developer 3 adheres to this peeling off roller 15, in addition to
the stirring effect described with respect to the peeling off
roller 14 illustrated in FIG. 16, a stirring mechanism is also
generated between the poles alternately arranged in the axial
direction of the peeling off roller 15, thus more effectively
mixing and stirring the developer 3.
Further, in a peeling off roller 16 illustrated in FIG. 17(b), the
N and S poles may be slightly separated from each other in the
axial direction thereof, or in a peeling off roller 17 illustrated
in FIG. 17(c), the N and S poles may be separated from each other
such that the poles of the same polarity overlap with each other in
the circumferential direction thereof.
Now, a result of an experiment made using a concrete example of the
developing device 2 according to the above-described embodiment is
described. Using the developing device 2 of FIG. 15, 20 prints were
made for the test chart 60 in which black stripes are repeatedly
formed as illustrated in FIG. 11 so that the toner 3a is consumed
in particular places of the developing sleeve 4 in the width
direction thereof, i.e., correspondingly to the black stripes.
Thereafter, an image having a half-tone of about ID 0.2-0.5
(measured by a reflecting density measuring device) over the entire
surface thereof was printed for 20 prints, and the image density
unevenness was evaluated for ranking the degree of the image
density unevenness. The developing conditions were set as specified
in the following Table 2.
Table 2
Diameter of the photoconductive drum: 30 mm;
Linear speed of the photoconductive drum: 100 mm/sec;
Gap Gp between the developing sleeve and the photoconductive drum:
0.4 mm;
Gap Gd1 between the developing sleeve and the doctor: 0.4 mm;
Gap Gd2 between the developing sleeve and the pre-doctor: 0.6
mm;
Gap Gh between the developing sleeve and the peeling off roller:
0.4 mm;
Diameter of the developing sleeve: 16 mm;
Linear speed ratio of the developing sleeve relative to the
photoconductive drum: 2.5;
Linear speed ratio of the peeling off roller relative to the
developing sleeve: 0.8;
Material of the carrier: magnetite;
Particle diameter of the carrier: about 50 .mu.m;
Material of the toner: resin in which a magnetic member is
mixed;
Particle diameter of the toner: 6.5-9.5 .mu.m.
FIGS. 18(a)-18(e) are diagrams for explaining the degree of the
image density unevenness, each illustrating a half-tone image
having residual black stripes 52a of different density, which was
formed on a sheet 52. The image density unevenness of FIG. 18(a) is
given a rank 2, that of FIG. 18(b) a rank 3, that of FIG. 18(c) a
rank 3.5, that of FIG. 18(d) a rank 4, and that of FIG. 18(e) a
rank 5. The higher the rank, the image density unevenness is less.
The image density unevenness of rank 3 is the one obtained by
conventional apparatuses.
In the experiments made under the conditions as above, it was
confirmed that the image density unevenness has been improved.
Specifically, with the peeling off roller 14 illustrated in FIG.
16, images of rank 3 or 3.5 were obtained, and with the peeling off
rollers 15, 16, and 17 illustrated in FIGS. 17(a), 17(b) and 17(c),
images of rank 3.5 or 4 were obtained.
Further, with respect to the developing device according to the
above-described embodiment, the inventors of the present invention
have found that the ratio between the linear speed of the
developing sleeve 4 and that of the peeling off roller 14 plays an
important role in generating a circulating movement of the
developer 3 around the peeling off roller 14 and in sufficiently
accelerating the frictional charging of the developer 3 with each
other. Therefore, an independent variable speed driving device (not
shown) that rotates the peeling off roller 14 with the linear speed
thereof made variable may be provided inside a driving part of the
developing device, such that the variable speed driving device is
controlled by the engine control part 100 illustrated in FIG. 7.
The variable speed driving device may include a stepping motor for
a driving source. An AC motor or a servo motor may also be used for
the driving source of the variable speed driving device.
In order to confirm an effect of the ratio between the linear speed
of the developing sleeve 4 and that of the peeling off roller 14,
an experiment to form images while changing the above ratio was
performed under the following conditions of Table 4.
Table 4
Linear speed of the photoconductive drum: 120 mm/sec;
Gap Gp between the developing sleeve and the photoconductive drum:
0.3-0.5 mm;
Gap Gd1 between the developing sleeve and the doctor: 0.3-0.5
mm;
Gap Gd2 between the developing sleeve and the pre-doctor: 0.5-1.5
mm;
Gap Gh between the developing sleeve and the peeling off roller:
0.3-1.2 mm;
Diameter of the developing sleeve: 16 mm;
Diameter of the peeling off roller: 7 mm;
Linear speed ratio of the developing sleeve relative to the
photoconductive drum: 1.5-3.0.
As a result of the above experiments, it was found that under the
condition of the linear speed of the developing sleeve 4 at
S(mm/sec) and the linear speed of the peeling off roller 14 at
T(mm/sec), by setting the ratio .epsilon. of T/S so as to satisfy a
condition: 5<.epsilon.<1.5, the frictional charging of the
developer 3 with each other is effectively made in the developer
accommodating part S at the gap between the developing sleeve 4 and
the peeling off roller 14. This is because, the quantity of the
carrier which is set in the apparatus being fixed, if at least the
linear speed ratio between the developing sleeve 4 and the peeling
off roller 14 is within the above range of Table 4, an appropriate
quantity of the toner is taken into the developer, and thereby the
conveying speed and the volume of the toner on the developing
sleeve 4 change such that the frictional charging of the developer
3 is effectively made.
Also, it was found that in the developing device of the
above-described embodiment, the quantity of the toner 3a to be
taken into changes according to a change of the coagulation degree
of the toner 3a due to the environmental conditions, thereby
causing a change in the conveying speed and the volume of the toner
3a. The coagulation degree of the toner 3a changes according to a
change of the temperature and humidity, and as indicated in FIGS. 8
and 9, the coagulation degree rises under a high temperature
condition and a high humidity condition as well. A higher
coagulation degree indicates that the toner 3a tends to be easily
hardened.
Accordingly, by providing a temperature sensor (not shown) for
measuring an ambient temperature in the vicinity of the
photoconductive drum 1 and by increasing the rotation number of the
peeling off roller 14 with the above variable speed driving device
when the temperature rises so as to increase the linear speed of
the peeling off roller 14, the developer 3 can be sufficiently
mixed and stirred and the frictional charging of the developer 3
with each other can be sufficiently accelerated.
Furthermore, in the digital image forming apparatuses such as the
printer according to the above-described embodiment, it is also
possible to change the linear speed of the peeling off roller 14 by
obtaining information of the quantity of the toner 3a to be
consumed in the development based upon the ratio of an image
portion of an original for printing, which is obtained from an
image signal for the original, and by changing the linear speed of
the peeling off roller 14 according to the quantity of the toner 3a
to be consumed. Specifically, when the toner density is decreased
as a result of forming an image having a high image portion ratio,
because a relatively large amount of the toner 3a is supplied and
thereby the frictional charging of the developer 3 must be
aggressively made, the peeling off roller 14 is controlled such
that the linear speed thereof is increased. On the other hand, when
the toner density is kept constant as a result of forming an image
having a relatively low image portion ratio, because the frictional
charging of the developer 3 needs not be aggressively made for
avoiding earlier deterioration of the developer 3, the peeling off
roller 14 is controlled such that the linear speed thereof is kept
the same or decreased.
Also, it was found that if the above ratio .epsilon. becomes
greater than 1.5 by increasing the linear speed of the peeling off
roller 14, not only is the deterioration of the developer 3
accelerated, but also the developer 3 is regulated to be taken into
the developer accommodating part S, thereby decreasing the toner
density to be less than a desired level. In contrast, if the ratio
.epsilon. becomes smaller than 0.5 by decreasing the linear speed
of the peeling off roller 14, the mixing and stirring effect was
not obtained and uneven supplying of the toner 3a was confirmed on
the image. The above-described control applied to the peeling off
roller 14 can be also applied to the peeling off rollers 15, 16,
and 17 to obtain substantially the same effect.
FIG. 19 is a schematic drawing illustrating a developing device
according to another embodiment of the present invention. In FIG.
19, the parts similar to those of the previous embodiment
illustrated in FIGS. 2 and 3 are denoted by like references, and
because the function thereof is substantially the same, the
description thereof is omitted. Also, an image forming apparatus
using the developing device of this embodiment can be controlled by
the control part illustrated in FIG. 7.
In the developing device of this embodiment, a peeling off member
12 formed in a grid-like flat plate is arranged in the developer
accommodating part S downstream of the pre-doctor 7a in the
rotating direction of the developing sleeve 4. The peeling off
member 12 is uniformly flat in the longitudinal direction thereof
and a gap Gh relative to the developing sleeve 4 and an interval L2
relative to the pre-doctor 7a are kept constant (see FIG. 22).
In the developing device of FIG. 19, the toner 3a supplied from the
toner hopper 8 formed upstream of the pre-doctor 7a passes the
pre-doctor 7a to reach the peeling off member 12. The developer
attempting to move toward the doctor 6 caused by the conveying
force of the developing sleeve 4 is once peeled off the developing
sleeve 4 by the peeling off member 12. The developer peeled off by
the peeling off member 12 is replaced and mixed with the developer
accommodated in the developer accommodating part S and is then
carried again by the developing sleeve 4 by a magnetic force. With
this replacement and mixture of the developer, the developer is
stirred such that the toner density becomes uniform and also the
toner charging is accelerated.
As described above, according to the above-described embodiment, by
accelerating the replacement and mixture of the developer on the
developing sleeve 4 with the one in the developer accommodating
part S, earlier deterioration of the developer due to a decrease of
a charging capability of the carrier in the developer is prevented.
Furthermore, even when the toner is unevenly supplied to the
developing sleeve 4 in the longitudinal direction thereof, the
developer in which the toner is uniformly distributed can be
conveyed to the developing area, thereby enabling development of an
image without causing uneven image density.
The peeling off plate 12 formed in a grid-like flat plate is
disposed so as to be in close proximity to and to have the gap Gh
relative to a surface of the developing sleeve 4.
Therefore, a space for enabling the developer to freely move
therein can be realized in the developer accommodating part S at a
position separated from a surface of the developing sleeve 4.
Accordingly, the developer blocked by the doctor 6 freely moves in
the developer accommodating part S to the side of the toner
supplying opening 8a without being obstructed. Therefore, the toner
density control function of the developer, which is realized by
changing the condition of taking the toner into the developer by
changing the contact condition of the developer thus moved to the
side of the toner supplying opening 8a with the toner supplied from
the toner hopper 8, can be securely maintained.
Now, a concrete example of the developing device of the
above-described embodiment and a result of an experiment made using
the developing device according to the example are described. Using
the developing device illustrated in FIGS. 19 and 20 prints were
made with a test chart having an image in which black stripes are
formed at intervals such that the toner consumption varies in the
longitudinal direction of the developing sleeve 4. Thereafter,
another 20 prints were made using a test chart having an image with
an even half tone over the entire surface thereof. The developing
conditions were substantially the same as the ones indicated in
Table 1.
For the peeling off member, flat plates 12a and 12b of a
non-magnetic member formed in a grid-like shape as illustrated in
FIGS. 20 and 21 were used. The developer on the developing sleeve 4
is peeled off the developing sleeve 4 by the peeling off members
12a and 12b through the grid holes thereof. The gap Gh between the
peeling off member 12 and the developing sleeve 4 was set to 0.3 mm
and the interval L2 between the peeling off member 12 and the
pre-doctor 7a was set to 10 mm (see FIG. 22).
According to the result of the experiment made under the above
conditions, the developer on the developing sleeve 4 was peeled off
the developing sleeve 4 to be replaced and mixed with the one in
the developer accommodating part S, such that the toner density of
the developer was made uniform, and thereby a good image having a
uniform image density was obtained.
In the experiment with the developing device of the above-described
embodiment, by configuring the developing device such that the gap
Gh between the peeling off member 12 and the developing sleeve 4
and the gap Gd2 between the developing sleeve 4 and the pre-doctor
7a satisfy the relation: 0<<Gh<Gd2, a good mixing and
stirring capability was realized.
Further, because only an upper part layer of the developer 3 on the
developing sleeve 4 was peeled off by the peeling off member 12 of
a grid-like flat plate, the self toner density control mechanism to
change the condition of taking the toner 3a into the developer 3 by
changing the contact condition of the conveyed developer 3b with
the toner 3a from the toner hopper 8 at the toner supplying opening
8a was stably maintained.
FIG. 23 is a schematic drawing illustrating a developing device
according to still another embodiment of the present invention. In
FIG. 23, the parts similar to those of the previous embodiment
illustrated in FIGS. 2 and 3 are denoted by like references, and
because the function thereof is substantially the same, the
description thereof is omitted. Also, an image forming apparatus
using the developing device of this embodiment can be controlled by
the control part illustrated in FIG. 7.
In the developing device of this embodiment, a stirring comb member
20 is provided in the developer accommodating part S as a developer
stirring member downstream of the pre-doctor 7a and upstream of the
doctor 6 in the developer conveying direction of the developing
sleeve 4. The stirring comb member 20 is shaped so as to have a
uniform width and thickness in the longitudinal direction thereof,
and the stirring comb member 20 is fixed in the developer
accommodating part S so as to keep constant a distance L2 from the
pre-doctor 7a and an interval Gk between a tip end of the stirring
comb member 20 and a surface of the developing sleeve 4 (see FIG.
24).
In the developing device according to the above-described
embodiment, an upper layer part of the conveyed developer on the
developing sleeve 4 conveyed into the developer accommodating part
S is stirred by the stirring comb member 20 opposing the developing
sleeve 4 in a non-contacting manner at a position adjacent to the
toner hopper 8 in the developer accommodating part S. Due to this
stirring of the developer, the conveyed developer on the developing
sleeve 4 and the accommodated developer in the developer
accommodating part S are mixed and stirred with each other. Also,
due to the above stirring of the developer, the toner 3a taken from
the toner hopper 8 into the upper layer part of the developer on
the developing sleeve 4 is stirred and mixed with the developer
such that the toner density of the developer is made uniform.
Thereby, the developer having a uniform toner density is carried on
the developing sleeve 4 and conveyed to the developing area so as
to be used for a development of a latent image on the
photoconductive drum 1.
According to the above-described embodiment, because the stirring
comb member 20 stirs a part (the upper layer part) of the developer
on the developing sleeve 4, the conveying state of the developer on
the developing sleeve 4 is not disturbed and a stable self toner
density control mechanism is maintained. Further, because of the
mixing and stirring of the developer with the stirring comb member
20, background soiling and decrease in the image density due to
deterioration of the developer with a lapse of time are prevented,
and at the same time a good development having no uneven image
density in the axial direction of the developing sleeve 4 can be
realized.
Now, a concrete example of the developing device according to the
above-described embodiment and a result of an experiment made with
the developing device according to the example are described. The
developing device illustrated in FIG. 24 was used in the experiment
and the experiment conditions were set as indicated in the
following Table 5.
Table 5
Diameter of the photoconductive drum: 30 mm;
Linear speed of the photoconductive drum: 120 mm/sec;
Gap Gp between the developing sleeve and the photoconductive drum:
0.3-0.5 mm;
Gap Gd1 between the developing sleeve and the doctor: 0.3-0.5
mm;
Gap Gd2 between the developing sleeve and the pre-doctor: 0.5-1.5
mm;
Diameter of the developing sleeve: 16 mm;
Linear speed ratio of the developing sleeve relative to the
photoconductive drum: 1.5-3.0;
Material of the toner: magnetite or steel;
Particle diameter of the toner: 40-50 .mu.m;
Volume of a magnetic member in the toner: 15-40 wt %;
Volume of silica in the toner: 0.5-1.0 wt %;
Covered ratio of the toner with the carrier: 50-120%;
Q/M: 10-30 .mu.c/g.
FIG. 24 is a schematic drawing indicating an arrangement position
of the stirring comb member 20. The gap Gk between the stirring
comb member 20 and the developing sleeve 4 was set to 0.3 mm and
the distance L2 between the stirring comb member 20 and the
pre-doctor 7a to 1 mm.
FIG. 25 is a perspective view of the stirring comb member 20 used
in this embodiment. The stirring comb member 20 includes a series
of comb tooth 20a at the side opposing the developing sleeve 4. The
interval Pk between the tips of neighboring two comb tooth 20a was
set to 2 mm.
Using the developing device configured as described above, first,
20 prints were made for the test chart 60 illustrated in FIG. 11,
in which black stripes are formed at intervals such that the toner
consumption varies in a direction perpendicular to a surface moving
direction of the developing sleeve 4 (indicated by the arrow G in
FIG. 11), i.e., the image width direction of the chart 60.
Thereafter, another 20 prints were made using another test chart of
an image having an even half-tone over the entire surface thereof.
According to a result of the experiment, the toner density of the
developer 3 was made uniform with respect to the image width
direction because of the stirring comb member 20, and thereby good
half-tone images having no image density unevenness were obtained.
In contrast, with the developing device in which the stirring comb
member 20 was not provided, uneven image density was observed in
the half-tone images.
From the above experiment, it was found that when developing a test
chart in which black stripes are formed such that the toner
consumption varies in the longitudinal direction of the developing
sleeve 4, if the chart is developed without using the stirring comb
member 20, a good image cannot be obtained because of uneven toner
density in the image width direction, and that on the other hand,
with the provision of the stirring comb member 20, the uneven toner
density in the image width direction can be avoided.
More specifically, the toner 3a supplied from the upstream of the
pre-doctor 7a in the developer conveying direction passes the gap
between the developing sleeve 4 and the pre-doctor 7a together with
the conveyed developer on the developing sleeve 4 to reach the
stirring comb member 20. The conveyed developer containing the
toner 3a thus supplied is stirred by a resisting force generated by
the stirring comb member 20 when the developer is conveyed by the
developing sleeve 4, and at the same time, when passing the
stirring comb member 20, the developer hits the series of comb
tooth 20a to be separated to both sides of each comb tooth 20a
sandwiching the comb tooth 20a, so that each separated developer is
mixed with another developer separated by the neighboring comb
tooth 20a in each space between the neighboring comb teeth 20a.
Because of this mixing of the developer in the lateral direction,
the toner density in the developer is made uniform in the axial
direction of the developing sleeve 4 and charging of the toner 3a
is accelerated. As a result, even when the toner 3a is unevenly
supplied in the longitudinal direction of the developing sleeve 4,
the toner density of the developer is made uniform in the
longitudinal direction of the developing sleeve 4 and thereby a
good image can be obtained.
Further, because the stirring comb member 20 is arranged with the
gap Gk relative to the developing sleeve 4 so as to stir a part
(the upper layer part) of the conveyed developer on the developing
sleeve 4, the movement of the conveyed developer on the developing
sleeve 4 in the developer accommodating part S is not obstructed.
Accordingly, there is no possibility that the self toner density
control mechanism fails. In particular, because the developer
stirring member is shaped to have comb teeth, the movement of the
developer obstructed by the doctor 6 in the developer accommodating
part S is hardly obstructed. Therefore, the toner 3a taken into the
developer can be stirred while securely maintaining the mechanism
of the self toner density control.
It was also found that a good stirring capability can be realized
by using a nonmagnetic member for the stirring comb member 20 and
by setting the gap Gk so as to satisfy the condition:
0<Gk<Gd2. By thus setting the gap Gk, at least a part of the
toner 3a supplied from the regulating position of the pre-doctor 7a
securely passes the spaces between the comb tooth 20a and comb
tooth 20a of the stirring comb member 20. Therefore, the supplied
toner 3a can be securely stirred in the lateral direction.
It was also found that a good stirring capability can be realized
by setting the interval Pk between the tip ends of neighboring two
comb tooth 20 to satisfy the condition. 0<Pk<5 mm. In this
embodiment, the interval Pk is set to be smaller than 5 mm, and
with this setting, uneven toner density in the image width
direction was satisfactorily avoided.
FIG. 26 is a schematic drawing illustrating a developing device
according to still another embodiment of the present invention. The
developing device is configured in substantially the same manner as
the one of the previous embodiment illustrated in FIG. 23 except
for the following differences. In the developing device of this
embodiment, in place of the stirring comb member 20, a sheet member
21 as an example of a flexible plate member is provided at a
position adjacent to the toner hopper 8 in the developer
accommodating part S so as to oppose a surface of the developing
sleeve 4 and to contact a part of the developer carried on the
developing sleeve 4, that contains the toner 3a taken from the
toner hopper 8. In the developing device of FIG. 23, the base plate
surface of the toner supplying opening 8a is slightly curved like a
saucer. In contrast, in the developing device of this embodiment,
the base plate surface of the toner supplying opening 8a is shaped
so as to straightly decline toward the developing sleeve 4 from the
toner hopper 8. Further, at a horizontal cross-section of the toner
hopper 8, the area of the toner hopper 8 is smaller than that of
the developing device of FIG. 23. Furthermore, in the developing
device of FIG. 23, the developer accommodating case 7 is made such
that the border parts of the upper wall, the side wall, and the
bottom wall (the pre-doctor 7a) surrounding the developer
accommodating part S are respectively curved. In contrast, in the
developing device of FIG. 26 according to this embodiment, the
developer accommodating case 7 is made such that the border part of
the side wall and the bottom wall (the pre-doctor 7a) are sharply
bent. The construction and the operation of the developing device
except for the above-described differences are substantially the
same as those of the developing device of FIG. 23, and therefore
the description thereof is omitted.
More concrete examples of the developing device of this embodiment
are now described. FIG. 27 is a partly enlarged schematic drawing
illustrating the developer accommodating part S and a toner take-in
part of the developing device. In the developing device, the sheet
member 21 is provided to a side surface of the pre-doctor 7a at the
side of the developer accommodating part S. The sheet member 21 in
this embodiment includes a polyurethane seal. However, any
sheet-like or plate-like member having flexibility can be used for
the sheet member 21.
The sheet member 21 is pasted to an internal surface of the
pre-doctor 7a such that an end part thereof at the side of the
developing sleeve 4 is formed into a free end part 21a and the free
end part 21a is bent toward the downstream side of the developer
conveying direction by being pulled by the developer carried and
conveyed by the developing sleeve 4. The position of the tip end of
the free end part 21a when the free end part 21a is thus bent
defines a third regulating position. The sheet member 21 is bent or
restored due to its flexibility according to a pressing force
exerted by the toner 3a which has been taken into the developer
accommodating part S through the second regulating position with
the pre-doctor 7a. The toner 3a which has been excessively taken
into the developer is prevented from being conveyed toward an area
at the downstream side in the developer conveying direction with
the developing sleeve 4. At the same time, at the third regulating
position, the toner density in the developer is made uniform in the
image width direction which is perpendicular to the developer
conveying direction by the developing sleeve 4. Thus, the excessive
toner 3a is removed and the toner 3a which has been uniformly
distributed in the image width direction is taken into the conveyed
developer on the developing sleeve 4, and the toner density in the
conveyed developer on the developing sleeve 4 is further made
uniform at the regulating position by the doctor 6 so as to be used
for development.
Good images were obtained without having uneven image density in
the image width direction in an experiment made using a developing
device provided with the sheet member 21 as described above.
FIG. 28 is an enlarged schematic drawing illustrating the developer
accommodating part S and a toner take-in part of the developing
device, that includes another example of the sheet member.
According to this example of the sheet member, a free end part 22a
of a sheet member 22 is longer than a shortest length to reach a
surface of the developing sleeve 4. Because of this length of the
free end part 22a, a tip end of the free end part 22a contacts a
surface of the developing sleeve 4, and with a movement of the
developing sleeve 4, the free end part 22a is bent toward the
downstream side in the developer moving direction by being pulled
by the developer carried and conveyed by the developing sleeve 4.
The position of the tip end of the free end part 22a when the free
end part 22a is thus bent defines the third regulating position.
The toner 3a carried and conveyed by the developing sleeve 4 is
moved relative to the sheet contacting member 22 while contacting
the sheet member 22. The excessive toner 3a is thus regulated at
the third regulating position and at the same time the toner
density in the developer is made uniform in the image width
direction perpendicular to the developer conveying direction by the
developing sleeve 4.
Thus, the excessive toner 3a is removed and the toner 3a which has
been uniformly distributed in the image width direction is taken
into the developer on the developing sleeve 4, and the developer
containing the uniformly distributed toner 3a passes the regulating
position by the doctor 6 to be used for development.
Good images were obtained without having uneven image density in
the image width direction in an experiment made using the
developing device provided with the sheet member 22 as described
above.
FIG. 29 is an enlarged schematic drawing illustrating the developer
accommodating part S and a toner take-in part of the developing
device, in which another example of the sheet member is included.
According to this example, a free end part 23a of a sheet member 23
is made longer than a shortest length to reach a surface of the
developing sleeve 4 as in the immediately above example. In
addition, the thickness of the sheet member 23 is made such that
the free end part 23a is bent by a pressure caused by the conveyed
developer on the developing sleeve 4, and thereby a surface of the
free end part 23a contacts the conveyed developer on the developing
sleeve 4 uniformly in the image width direction and for a
relatively long distance in the developer conveying direction. The
position of this surface contacting part of the free end part 23a
of the sheet member 23 defines the third regulating position. With
this configuration, the excessive toner 3a is removed and the toner
3a uniformly distributed in the image width direction is taken into
the developer on the developing sleeve 4, and the developer
containing thus uniformly distributed toner 3a passes the
regulating position by the doctor 6 so as to be used for
development.
Good images were obtained without having uneven image density in
the image width direction in an experiment made using the
developing device provided with the sheet member 23 as described
above.
FIG. 30 is an enlarged schematic drawing illustrating the developer
accommodating part S and a toner take-in part of the developing
device, in which another example of the sheet member is included.
According to this example, a free end part 24a of a sheet member 24
is made longer than a shortest length to reach a surface of the
developing sleeve 4 as in the immediately above example. In
addition, the length of the free end part 24a of the sheet member
24 is made such that the free end part 24a is bent by a pressure
caused by the conveyed developer on the developing sleeve 4 and
such that the free end part 24a contacts the conveyed developer on
the developing sleeve 4 uniformly in the image width direction and
for a relatively long distance in the developer conveying
direction. This surface contacting part of the free end part 24a of
the sheet member 24 forms the third regulating position. With this
configuration, the excessive toner 3a is removed and the toner 3a
uniformly distributed in the image width direction is taken into
the developer on the developing sleeve 4, and the developer
containing thus uniformly distributed toner 3a passes the
regulating position by the doctor 6 so as to be used for
development.
Good images were obtained without having uneven image density in
the image width direction in an experiment made using a developing
device provided with the sheet member 24 as described above.
In the developing device of FIG. 30, the end part of the sheet
member 24 opposite the free end part 24a is made longer than a
length necessary for fixing this end part to the side of the
pre-doctor 7a at the side of the developer accommodating part S.
Specifically, this end part is made to extend over the internal
surface of the pre-doctor 7a in a perpendicular direction relative
to a surface of the developing sleeve 4 and that of a part of the
side wall of the developer accommodating part S, which extends from
the pre-doctor 7a upward by being bent. The sheet member 24 is
pasted to the internal surface of the pre-doctor 7a to be bent such
that the sheet member 24 is separated from the position of the
internal surface of the pre-doctor 7a where the pre-doctor 7a is
bent. With this configuration, the developer can be more smoothly
circulated in the developer accommodating part S. Thus, even if the
shape of the internal surface of the developer accommodating part S
is made to include such a bending portion and is not smooth enough
to circulate the developer, such a bending portion can be covered
by the sheet member 24 so that the developer can be smoothly
circulated in the developer accommodating space S.
FIG. 31 is an enlarged schematic drawing illustrating the developer
accommodating part S and a toner take-in part of the developing
device, in which another example of the sheet member is included.
According to this example, a free end part 25a of a sheet member 25
is made sufficiently longer than a shortest length to reach a
surface of the developing sleeve 4, such that the free end part 25a
is rolled up and an outer circumferential part 25b at a curved part
of the rolled up free end part 25a contacts the conveyed developer
on the developing sleeve 4. With this rolling up configuration, the
sheet member 25 is strengthened, and the position of the contacting
part of the free end part 25a of the sheet member 25 defines the
third regulating position. With this configuration, the excessive
toner 3a is removed and the toner 3a uniformly distributed in the
image width direction is taken into the developer on the developing
sleeve 4, and the developer containing thus uniformly distributed
toner 3a passes the regulating position by the doctor 6 so as to be
used for development.
Good images were obtained without having uneven image density in
the image width direction in an experiment made using the
developing device provided with the sheet member 25 as described
above.
As described above, in the developing device according to the above
embodiment, the sheet members 21-25 regulate the take-in of the
toner 3a into the developer and make the toner density in the
developer uniform in the image width direction such that uneven
image density is prevented.
Further, with respect to the stirring comb member 20 and the sheet
members 21-25, the toner density is made uniform in the
longitudinal direction of the developing sleeve 4 only by fixing
these members in the developer accommodating part S. Therefore, it
is not necessary to provide and drive by a motor a member for
stirring the developer in the developer accommodating part S.
Accordingly, an effect of avoiding uneven image density in the
image width direction can be obtained at relatively low cost.
Numerous additional modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the present invention may be practiced otherwise than as
specifically described herein.
The present application claims priority and contains subject matter
related to Japanese Patent Applications No. 11-174693, No.
11-187727, No. 11-188219, No. 11-269348, No. 11-272551, and No.
xx-xxxxxx, respectively filed in the Japanese Patent Office on Jun.
21, 1999, Jul. 1, 1999, Jul. 1, 1999, Sep. 22, 1999, Sep. 27, 1999,
and May xx, 2000, and the entire contents of which are hereby
incorporated herein by reference.
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